    Network Working Group                                            C. Adie
    Request for Comments: 1614        Edinburgh University Computing Service
    RARE Technical Report: 8                                        May 1994
    Category: Informational

                    Network Access to Multimedia Information

    Status of this Memo

       This memo provides information for the Internet community.  This memo
       does not specify an Internet standard of any kind.  Distribution of
       this memo is unlimited.

    Abstract

       This report summarises the requirements of research and academic
       network users for network access to multimedia information.  It does
       this by investigating some of the projects planned or currently
       underway in the community.  Existing information systems such as
       Gopher, WAIS and World-Wide Web are examined from the point of view
       of multimedia support, and some interesting hypermedia systems
       emerging from the research community are also studied.  Relevant
       existing and developing standards in this area are discussed.  The
       report identifies the gaps between the capabilities of
       currentlydeployed systems and the user requirements, and proposes
       further work centred on the World-Wide Web system to rectify this.

       The report is in some places very detailed, so it is preceded by an
       extended summary, which outlines the findings of the report.

    Publication History

       The first edition was released on 29 June 1993.  This second edition
       contains minor changes, corrections and updates.

    Table of Contents

        Acknowledgements                                                2
        Disclaimer                                                      2
        Availability                                                    3
        0. Extended Summary                                             3
        1. Introduction                                                10
          1.1. Background                                              10
          1.2. Terminology                                             11
        2. User Requirements                                           13
          2.1. Applications                                            13
          2.2. Data Characteristics                                    18

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    RFC 1614        Network Access to Multimedia Information        May 1994

          2.3. Requirements Definition                                 19
        3. Existing Systems                                            24
          3.1. Gopher                                                  24
          3.2. Wide Area Information Server                            30
          3.3. World-Wide Web                                          34
          3.4. Evaluating Existing Tools                               42
        4. Research                                                    47
          4.1. Hyper-G                                                 47
          4.2. Microcosm                                               48
          4.3. AthenaMuse 2                                            50
          4.4. CEC Research Programmes                                 51
          4.5. Other                                                   53
        5. Standards                                                   55
          5.1. Structuring Standards                                   55
          5.2. Access Mechanisms                                       62
          5.3. Other Standards                                         63
          5.4. Trade Associations                                      66
        6. Future Directions                                           68
          6.1. General Comments on the State-of-the-Art                68
          6.2. Quality of Service                                      70
          6.3. Recommended Further Work                                71
        7. References                                                  76
        8. Security Considerations                                     79
        9. Author's Address                                            79

    Acknowledgements

       The following people have (knowingly or unknowingly) helped in the
       preparation of this report: Tim Berners-Lee, John Dyer, Aydin Edguer,
       Anton Eliens, Tony Gibbons, Stewart Granger, Wendy Hall, Gary Hill,
       Brian Marquardt, Gunnar Moan, Michael Neuman, Ari Ollikainen, David
       Pullinger, John Smith, Edward Vielmetti, and Jane Williams.  The
       useful role which NCSA's XMosaic information browser tool played in
       assembling the information on which this report was based should also
       be acknowledged - many thanks to its developers.

       All trademarks are hereby acknowledged as being the property of their
       respective owners.

    Disclaimer

       This report is based on information supplied to or obtained by
       Edinburgh University Computing Service (EUCS) in good faith.  Neither
       EUCS nor RARE nor any of their staff may be held liable for any
       inaccuracies or omissions, or any loss or damage arising from or out
       of the use of this report.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       The opinions expressed in this report are personal opinions of the
       author.  They do not necessarily represent the policy either of RARE
       or of ECUS.

       Mention of a product in this report does not constitute endorsement
       either by EUCS or by RARE.

    Availability

       This document is available in various forms (PostScript, text,
       Microsoft Word for Windows 2) by anonymous FTP through the following
       URL:

        ftp://ftp.edinburgh.ac.uk/pub/mmaccess/

        ftp://ftp.rare.nl/rare/pub/rtr/rtr8-rfc.../

        Paper copies are available from the RARE Secretariat.

    0. Extended Summary

       Introduction

       This report is concerned with issues in the intersection of
       networked information retrieval, database and multimedia
       technologies.  It aims to establish research and academic user
       requirements for network access to multimedia data, to look at
       existing systems which offer partial solutions, and to identify
       what needs to be done to satisfy the most pressing requirements.

       User Requirements

       There are a number of reasons why multimedia data may need to be
       accessed remotely (as opposed to physically distributing the data,
       e.g., on CD-ROM).  These reasons centre on the cost of physical
       distribution, versus the timeliness of network distribution.  Of
       course, there is a cost associated with network distribution, but
       this tends to be hidden from the end user.

       User requirements have been determined by studying existing and
       proposed projects involving networked multimedia data.  It has
       proved convenient to divide the applications into four classes
       according to their requirements: multimedia database applications,
       academic (particularly scientific) publishing applications, cal
       (computeraided learning), and general multimedia information
       services.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       Database applications typically involve large collections of
       monomedia (non-text) data with associated textual and numeric
       fields. They require a range of search and retrieval techniques.

       Publishing applications require a range of media types,
       hyperlinking, and the capability to access the same data using
       different access paradigms (search, browse, hierarchical, links).
       Authentication and charging facilities are required.

       Cal applications require sophisticated presentation and
       synchronisation capabilities, of the type found in existing
       multimedia authoring tools.  Authentication and monitoring
       facilities are required.

       General multimedia information services include on-line
       documentation, campus-wide information systems, and other systems
       which don't conveniently fall into the preceding categories.
       Hyperlinking is perhaps the most common requirement in this area.

       The analysis of these application areas allows a number of
       important user requirements to be identified:

          o    Support for the Apple Macintosh, UNIX and PC/MS Windows
               environments.

          o    Support for a wide range of media types - text, image,
               graphics and application-specific media being most
               important, followed by video and sound.

          o    Support for hyperlinking, and for multiple access structures
               to be built on the same underlying data.

          o    Support for sophisticated synchronisation and presentation
               facilities.

          o    Support for a range of database searching techniques.

          o    Support for user annotation of information, and for user-
               controlled display of sequenced media.

          o    Adequate responsiveness - the maximum time taken to retrieve
               a node should not exceed 20s.

          o    Support for user authentication, a charging mechanism, and
               monitoring facilities.

          o    The ability to execute scripts.

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    RFC 1614        Network Access to Multimedia Information        May 1994

          o    Support for mail-based access to multimedia documents, and
               (where appropriate) for printing multimedia documents.

          o    Powerful, easy-to-use authoring tools.

       Existing Systems

       The main information retrieval systems in use on the Internet are
       Gopher, Wais, and the World-Wide Web.  All work on a client-server
       paradigm, and all provide some degree of support for multimedia data.

       Gopher presents the user with a hierarchical arrangement of nodes
       which are either directories (menus), leaf nodes (documents
       containing text or other media types), or search nodes (allowing some
       set of documents to be searched using keywords, possibly using WAIS).
       A range of media types is supported.  Extensions currently being
       developed for Gopher (Gopher+) provide better support for multimedia
       data.  Gopher has a very high penetration (there are over 1000 Gopher
       servers on the Internet), but it does not provide hyperlinks and is
       inflexibly hierarchical.

       Wais (Wide Area Information Server) allows users to search for
       documents in remote databases.  Full-text indexing of the databases
       allows all documents containing particular (combinations of) words to
       be identified and retrieved.  Non-text data (principally image data)
       can be handled, but indexing such documents is only performed on the
       document file name, severely limiting its usefulness.  However, WAIS
       is ideally suited to text search applications.

       World-Wide Web (WWW) is a large-scale distributed hypermedia system.
       The Web consists of nodes (also called documents) and links.  Links
       are connections between documents: to follow a link, the user clicks
       on a highlighted word in the source document, which causes the
       linkedto document to be retrieved and displayed.  A document can be
       one of a variety of media types, or it can be a search node in a
       similar sense to Gopher.  The WWW addressing method means that WAIS
       and Gopher servers may also be accessed from (indeed, form part of)
       the Web.  WWW has a smaller penetration than Gopher, but is growing
       faster.  The Web technology is currently being revised to take better
       account of the needs of multimedia information.

       These systems all go some way to meet the user requirements.

          o    Support for multiple platforms and for a wide range of media
               types (through "viewer" software external to the client
               program) is good.

          o    Only WWW has hyperlinks.

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          o    There is little or no support for sophisticated presentation
               and synchronisation requirements.

          o    Support for database querying tends to be limited to
               "keyword" searches, but current developments in Gopher and
               WWW should make more sophisticated queries possible.

          o    Some clients support user annotation of documents.

          o    Response times for all three systems vary substantially
               depending on the network distance between client and server,
               and there is no support for isochronous data transfer.

          o    There is little in the way of authentication, charging and
               monitoring facilities, although these are planned for WWW.

          o    Scripting is not supported because of security issues

          o    WWW supports a mail responder.

          o    The only system sufficiently complex to warrant an authoring
               tool is WWW, which has editors to support its hypertext
               markup language.

       Research

       There are a number of research projects which are of significant
       interest.

       Hyper-G is an ambitious distributed hypermedia research project at
       the University of Graz.  It combines concepts of hypermedia,
       information retrieval systems and documentation systems with aspects
       of communication and collaboration, and computer-supported teaching
       and learning.  Automatic generation of hyperlinks is supported, and
       there is a concept of generic structures which can exist in parallel
       with the hyperlink structure.  Hyper-G is based on UNIX, and is in
       use as a CWIS at Graz.  Gateways between Hyper-G and WWW exist.

       Microcosm is a PC-based hypermedia system developed at the University
       of Southampton.  It can be viewed as an integrating hypermedia
       framework - a layer on top of a range of existing applications which
       enables relationships between different documents to be established.
       Hyperlinks are maintained separately from the data.  Networking
       support for Microcosm is currently under development, as are versions
       of Microcosm for the Apple Macintosh and for UNIX.  Microcosm is
       currently being "commercialised".

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       AthenaMuse 2 is an ambitious distributed hypermedia authoring and
       presentation system under development by a university/industry
       consortium based at MIT.  It will have good facilities for
       presentation and synchronisation of multimedia data, strong authoring
       support, and will include support for networking isochronous data. It
       will be a commercial product.  Initial versions will support UNIX and
       X windows, with a PC/MS Windows version following.  Apple Macintosh
       support has lower priority.

       The "Xanadu" project is designing and building an "open, social
       hypermedia" distributed environment, but shows no sign of delivering
       anything after several years of work.

       The European Commission sponsors a number of peripherally relevant
       projects through its Esprit and RACE research programmes.  These
       programmes tend to be oriented towards commercial markets, and are
       thus not directly relevant.  An exception is the Esprit IDOMENEUS
       project, which brings together workers in the database, information
       retrieval and multimedia fields.  It is recommended that RARE
       establish a liaison with this project.

       There are a variety of other academic and commercial research
       projects which are also of interest.  None of them are as directly
       relevant as those outlined above.

       Standards

       There are a number of existing and emerging standards for structuring
       hypermedia applications.  Of these, the most important are SGML,
       HyTime, MHEG, ODA, PREMO and Acrobat.  All bar the last are de jure
       standards, while Acrobat is a commercial product which is being
       proposed as a de facto standard.

       SGML (Standard Generalized Markup Language) is a markup language for
       delimiting the logical and semantic content of text documents.
       Because of its flexibility, it has become an important tool in
       hypermedia systems.  HyTime is an ISO standardised infrastructure for
       representing integrated, open hypermedia documents, and is based on
       SGML.  HyTime has great expressive power, but is not optimised for
       run-time efficiency.  It is recommended that future RARE work on
       networked hypermedia should take account of the importance of SGML
       and HyTime.

       MHEG (Multimedia and Hypermedia information coding Experts Group) is
       a draft ISO standard for representing hypermedia applications in a
       platform-independent form.  It uses an object-oriented approach, and
       is optimised for run-time efficiency.  Full IS status for MHEG is
       expected in 1994.  It is recommended that RARE keep a watching brief

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       on MHEG.

       The ODA (Open Document Architecture) standard is being enhanced to
       incorporate multimedia and hypermedia features.  However, interest in
       ODA is perceived to be decreasing, and it is recommended that ODA
       should not form a basis for further RARE work in networked
       hypermedia.

       PREMO is a new work item in the ISO graphics standardisation
       community, which appears to overlap with MHEG and HyTime.  It is not
       clear that the PREMO work, which is at a very early stage, is
       worthwhile in view of the existence of those standards.

       Acrobat PDF is a format for representing multimedia (printable)
       documents in a portable, revisable form.  It is based on Postscript,
       and is being proposed by Adobe Inc (originators of Postscript) as an
       industry standard.  RARE should maintain awareness of this technology
       in view of its potential impact on multimedia information systems.

       There are various standards which have relevance to the way
       multimedia data is accessed across the network.  Many of these have
       been described in a previous report [1].  Two further access
       protocols are the proposed multimedia extensions to SQL, and the
       Document Filing and Retrieval protocol.  Neither of these are likely
       to have major significance for networked multimedia information
       systems.

       Other standards of importance include:

          o    MIME, a multimedia email standard which defines a range of
               media types and encoding methods for those types which are
               useful in a wider context.

          o    AVIs (Audio-Visual Interactive services) and the associated
               multimedia scripting language SMSL, which form a
               standardisation initiative within CCITT (now ITU-TSS) to
               specify interactive multimedia services which can be
               provided across telephone/ISDN networks.

       There are two important trade associations which are involved in
       standardisation work.  The Interactive Multimedia Association (IMA)
       has a Compatibility Project which is developing a specification for
       platform-independent interactive multimedia systems, including
       networking aspects.  A newly-formed group, the Multimedia
       Communications Forum (MMCF), plans to provide input to the standards
       bodies.  It is recommended that RARE become an Observing Member of
       the MMCF.  A third trade association - the Multimedia Communications
       Community of Interest - has also just been formed.

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       Future Directions

       Three common design approaches emerge from the variety of systems and
       standards analysed in this report.  They can be described in terms of
       distinctions between different aspects of the system:

          o    content is distinct from hyperstructure

          o    media type is distinct from media encoding

          o    data is distinct from protocol

       Distributed hypermedia systems are emerging from the
       research/development phase into the experimental deployment phase.
       However, the existing global information systems (Gopher, WAIS and
       WWW) are still largely limited to the use of external viewers for
       nontextual data.  The most significant mismatches between the
       capabilities of currently-deployed systems and user requirements are
       in the areas of presentation and quality of service (i.e.,
       responsiveness).

       Improving QOS is significantly more difficult than improving
       presentation capabilities, but there are a number of possible ways in
       which this could be addressed.  Improving feedback to the user,
       greater multi-threading of applications, pre-fetching, caching, the
       use of alternative "views" of a node, and the use of isochronous data
       streams are all avenues which are worth exploring.

       In order to address these problems, it is recommended that RARE seek
       to adapt and enhance existing tools, rather than develop new ones.

       In particular, it is recommended that RARE select the World-Wide Web
       to concentrate its efforts on.  The reasons for this choice revolve
       around the flexibility of the WWW design, the availability of
       hyperlinks, the existing effort which is already going into
       multimedia support in WWW, the fact that it is an integrating
       solution incorporating both WAIS and Gopher support, and its high
       rate of growth compared to Gopher (despite Gopher's wider
       deployment).  Gopher is the main competitor to WWW, but its
       inflexibly hierarchical structure and the absence of hyperlinks make
       it difficult to use for highly-interactive multimedia applications.

       It is recommended that RARE should invite proposals for and
       subsequently commission work to:

          o    Develop conversion tools from commercial multimedia
               authoring packages to WWW, and accompanying authoring
               guidelines.

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          o    Implement and evaluate the most promising ways of overcoming
               the QOS problem.

          o    Implement a specific user project using these tools, to
               validate that the facilities being developed are truly
               relevant to real applications.

          o    Use the experience gained to inform and influence the
               development of the WWW technology.

          o    Contribute to the development of PC/MS Windows and Apple
               Macintosh WWW clients, particularly in the multimedia data
               handling area.

       It is noted that the rapid growth of WWW may in the future lead to
       problems through the implementation of multiple, uncoordinated and
       mutually incompatible add-on features.  To guard against this trend,
       it may be appropriate for RARE, in coordination with CERN and other
       interested parties such as NCSA, to:

          o    Encourage the formation of a consortium to coordinate WWW
               technical development.

    1. Introduction

    1.1. Background

       This study was inspired by the realisation that while some aspects of
       distributed multimedia technology are being actively introduced into
       the European research community (for instance, audiovisual
       conferencing, through the MICE project), other aspects are receiving
       less attention.  In particular, one category in which there seems to
       be relatively little activity is providing solutions to ease remote
       access to multimedia resources (for instance, accessing stored
       audio/video clips or images, or indeed entire multimedia
       applications, across the network).  Few commercial products address
       this, and the relevance of existing standards in this area is
       unclear.

       Of the 50 or so research projects documented in the recent RARE
       distributed multimedia survey [1], only about six have a direct
       relevance to this application area.  Where stated in the survey, the
       main research effort in these projects is often directed towards the
       "difficult" problems, such as the transfer of isochronous data and
       the design and implementation of object-oriented multimedia
       databases, rather than towards user-oriented issues.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       This report is concerned with practical issues in the intersection of
       networked information retrieval, database and multimedia
       technologies.  It aims to establish actual user requirements in this
       area, to look at existing systems which offer partial solutions, and
       to identify what additional work needs to be done to satisfy the most
       pressing requirements.

    1.2. Terminology

       In order to discuss multimedia information systems, we need a
       consistent terminology.  The vocabulary defined below embodies some
       of the concepts of the Dexter hypertext reference model [2].  This
       model is sufficiently general to be useful for describing most of the
       facilities and requirements of the multimedia information systems
       described in this report.  (However, the Dexter model does not
       describe searchable index objects - it is not a database reference
       model.)

        anchor             An identified portion of a node.  E.g., in a text
                           node, an anchor might be a string of one or more
                           adjacent characters, while in an image node it
                           might be a rectangular area of the image.

        composite node     A node containing data of multiple media types.

        document           Often used loosely as a synonym for node.

        hyperdocument      We refer to a collection of related nodes,
                           linked internally with hyperlinks, as a
                           "hyperdocument".  Examples are a database of
                           medical images and associated text; a module
                           from a suite of teaching material; or an article
                           in a scientific journal.  A hyperdocument may
                           contain hyperlinks to other data which exists in
                           internally with hyperlinks, as a
                           "hyperdocument". Examples are a other
                           hyperdocuments, but can be viewed as largely
                           self-contained.  It is a highlevel "unit of
                           authoring", but is not necessarily perceived as
                           a distinct unit by a reader (although it may be
                           so perceived, particularly if it contains few
                           hyperlinks to outside entities).

        hyperlink          Set of one or more source anchors and one or
                           more target anchors.  Also known simply as a
                           "link".

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        isochronous (adjective) Describes a continuous flow of data which
                           is required to be delivered by the network under
                           critical time constraints.

        leaf node          A node which contains no source anchors.

        media type         An attribute of data which describes the general
                           nature of its expected presentation.  The value
                           of this attribute could be one of the following
                           (not exhaustive) list:

                           o Text

                           o Sound

                           o Image (e.g., a "photograph")

                           o Graphics (e.g., a "drawing")

                           o Animation (i.e., moving graphics)

                           o Movie (i.e., moving image)

        monomedia (adjective)   Said of data which is all of the same media
                           type.

        multimedia (adjective)  Said of data which contains different media
                           types.  This definition is stricter than general
                           usage, where "multimedia" is often  used as a
                           generic term for non-textual data, and where it
                           may even be used as a noun.

        physical media     Magnetic or optical storage.  Not to be confused
                           with media type!

        [simple] node      A monomedia object which may be retrieved and
                           displayed as a single unit.

        source anchor      An anchor which may be "actioned" by the user,
                           causing the node(s) containing the target
                           anchor(s) in the same hyperlink to be retrieved
                           and displayed.  This process is called
                           "traversing the link".

        target anchor      an anchor forming part of a hyperlink, whose
                           containing node is retrieved and displayed when
                           the hyperlink is traversed.

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    RFC 1614        Network Access to Multimedia Information        May 1994

    2. User Requirements

       User requirements in an area such as networking, which is subject to
       rapid technological change, are sometimes difficult to identify.  To
       an extent, technology leads applications, and users will exploit what
       is possible.

    2.1. Applications

       Awareness of the range of networked multimedia applications which are
       currently being envisaged by computer users in the academic and
       research community leads to a better understanding of the technical
       requirements.  This section outlines some projects which require
       remote access to multimedia information across research networks, and
       which are currently either at a preliminary stage or underway.  The
       projects are divided into broad categories according to their
       characteristics.

       Multimedia Databases

       Here are several examples of multimedia projects which have a
       "database" character.

       The Peirce Telecommunity Project

          This project centres on the construction of a multimedia (text and
          image) database of the works of the American philosopher Peirce,
          together with tools to process the data and to make it available
          over the Internet.  A sub-project at Brown University focuses on
          adapting existing client/server network tools for this purpose.
          The requirements for network access include facilities for
          structured viewing, intelligent retrieval, navigation, linking,
          and annotation, as well as for domainspecific processing.

       Museum Object Databases

          The RAMA (Remote Access to Museum Archives) project is funded
          under the EEC RACE II programme.  Its objective is to develop a
          system which allows museums to make multimedia information about
          their exhibits and archived material available over an ISDN
          network.  The requirements capture and technical architecture
          design phases are now complete, and a prototype system will be
          delivered in June 1993 to link the Ashmolean Museum (Oxford, GB),
          the Musee d'Orsay (Paris, FR) and the Museum Archeological
          National (Madrid, ES).  Image data is the main media type of
          interest, although video and sound may also play a part.

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       The Bristol Biomedical Videodisk Project

          The Bristol Biomedical Videodisc is a collection of Medical,
          Veterinary and Dental images.  The collection holds some 24,000
          still images and is continuously growing.  Textual information
          regarding the images is included as part of the database and this
          can be searched on any keyword, number or other data type, or a
          combination of any of these.  The images are currently delivered
          in analogue form on a videodisc, but many institutions are unable
          to afford the cost of videodisc players.  Investigations into
          making this image and text database available across the network
          are underway.

       ArchiGopher

          ArchiGopher is a Gopher server at the College of Architecture,
          University of Michigan, dedicated to the dissemination of
          architectural knowledge.  Presently in its infancy, ArchiGopher is
          intended to become a multimedia resource for all architecture
          faculty and students world-wide.  Some of the available or planned
          resources are:

                o The College's image bank.

                o The CAD group's collection of computer models (already
                  started).

                o The Doctoral Program's recent dissertation proposals and
                  abstracts.

                o Example archive of Kandinsky paintings.

                o Images of 3D CAD projects.

          The principal media type in ArchiGopher is image.  Files are
          stored in both TIFF and GIF format.

       Vatican Library Exhibit

          In January 1993, the US Library of Congress mounted an electronic
          version of the exhibition ROME REBORN:  THE VATICAN LIBRARY AND
          RENAISSANCE CULTURE.  The exhibition was subsequently processed by
          the University of Virginia Library. The text files were broken
          into individual captions associated directly with each image and a
          WAIS-searchable version of the object index generated.  This has
          been made available on Gopher by the University of Virginia
          Library.

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    RFC 1614        Network Access to Multimedia Information        May 1994

          This project is particularly interesting, as it demonstrates some
          limitations of the Gopher system.  The principal media types are
          image and text, and it is difficult to associate a caption with
          its image - each must be fetched separately, and using the XMosaic
          or xgopher client software it is not possible to tell which menu
          entry is the image and which the caption. (This may be a
          consequence of how the data has been configured for the Gopher
          server; if so, a requirement for better publishing tools may be
          indicated.)  Furthermore, searching the object index will result
          in a Gopher menu containing references to catalogue entries for
          relevant exhibits, but not to the online images of the exhibits
          themselves, which severely limits the usefulness of the index.

          It is interesting to note that during the preparation of this
          report, the Vatican Exhibition has been mounted on the WorldWide
          Web (WWW).  The hypermedia presentation on the Web is very much
          more attractive to use than the Gopher version.

       Jukebox

          Jukebox is a project supported by the EEC libraries program.  The
          project aims to evaluate a pilot service providing library users
          with on-line access to a database of digital sound recordings.
          The database will support multi-user access and use suitable
          storage media to make available sound recordings in a compressed
          format.  Users will access the service with a personal computer
          connected to a telematic network.

       Scientific Publishing

       There are several refereed electronic academic journals presently
       distributed on the Internet.  These tend to be text-only journals,
       and have not really addressed the issues of delivering and
       manipulating non-text data.

       Many scientific publishers have plans for electronic publishing of
       existing academic journals and conference proceedings, either on
       physical media or on the network.  The Journal of Biological
       Chemistry is now published on CD-ROM, for instance.  Some publishers
       view CD-ROM as an interim step to the ultimate goal of making
       journals available on-line on the Internet.

       The main types of non-text data which are envisaged are:

          o    Images.  In many cases, image data (a microphotograph, say)
               is central to an article.  Software which recognises that
               the text may be of secondary importance to the image is
               required.

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          o    Application-specific data.  The ChemLab and MoleculeLab
               applications are widely used, and the integration of
               corresponding data types with journal articles will enhance
               readers' ability to visualise molecular structures.
               Similarly, mathematics appearing in scientific papers could
               be represented in a form suitable for processing by
               applications such as Mathematica.  Mathematical content
               could then become a much more interactive and dynamic aspect
               of research publications.

          o    Tabular data.  The ability for a reader to extract tabular
               data from a research paper, to produce a graphical
               representation, to subset the data, and to further process
               it in a number of different ways, is viewed as an essential
               part of scientific electronic publishing.

          o    Movies.  The American Astronomical Society regularly
               publishes videos to go with its academic journals.
               Electronic publishing can improve on this "hard copy"
               publishing by integrating video data much more closely with
               the source article.

          o    Sound.  There is perhaps slightly less demand for audio
               information in scientific publishing, but the requirement
               does exist in particular specialities (such as acoustics and
               zoology journals).

       Access to academic journals using at least four different paradigms
       is envisaged.  Hierarchical access, perhaps using a traditional
       journal/volume/issue/article model, is perhaps the most obvious.
       Keyword searching (or full-text indexing) will be required.  Browsing
       is another useful and often underestimated access model - to support
       browsing it is essential that "eye-catching" data (unlikely to be
       textual) is prominently accessible. The final method of access is
       perhaps the most important - the use of interactive viewing tools.
       Such tools would enable navigation of hypermedia links within and
       between articles, with gateways to special-purpose applications as
       described above.  The use of these disparate access methods implies
       more than one structure being applied to the same underlying data.

       Standards, particularly SGML, are becoming important to publishers,
       and it is clear that the SGML-based HyTime standard will be a front
       runner in providing the kind of hypermedia facilities which are being
       envisaged.  However, progress towards a common SGML Document Type
       Definition (DTD) for scientific articles, even within individual
       publishing houses and for text-only documents, is slow.

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       A specific initiative involving interested parties will be required
       to formalise detailed requirements and to pilot standards in this
       area.  A preliminary demonstrator project, funded by publishers and
       by the British Library Research and Development Department, involves
       making about 30 sample scientific articles available over the
       SuperJANET network, using a range of different software products. The
       demonstrator project is being managed by IOP Publishing and is being
       carried out at Edinburgh University Computing Service.

       Existing tools, particularly WAIS and WWW, are relevant, but adequate
       security and charging mechanisms are required if commercial
       publishers are to use them.  Many research groups are now making the
       text of preprints and published research papers available on Gopher
       servers.

       It is interesting to note that the proceedings of the Multimedia 93
       conference run by the ACM will be published electronically (on CD
       ROM), using a multimedia document format designed specifically for
       the event.

       Computer-aided Learning

       The ready availability of user-friendly multimedia authoring tools
       such as AuthorWare Professional, Asymmetrix Multimedia Toolbook,
       Macromind Director and many more, has stimulated much interest in
       multimedia for computer-aided learning applications within the user
       community.  Sophisticated interactive multimedia courseware
       applications are being developed in many disparate subjects
       throughout the European academic community.  Users are now beginning
       to ask network technologists, "how can I make my multimedia
       application available to others across the network?".

       There is considerable interest in using the network to enhance
       delivery of multimedia teaching materials - for instance to allow
       students to take courses remotely (distance learning) and for their
       learning process to be supported, monitored and assessed remotely.

       The requirements which flow from this type of network application
       include the ability to identify and authenticate the students using
       the material, to monitor their progress, and to supply on-line
       assessment exercises for the student to complete.  Multimedia
       authoring tools allow very attractive presentation environments to be
       created, which encourages learning; this is viewed as essential by
       course developers.  Easy-to-use authoring tools (preferably existing
       commercial ones) are also essential.

       Finally, some learning applications involve simulations - examples
       include meteorological modelling and economic simulations.  Network

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       delivery of teaching materials should cope with this requirement
       (perhaps by acknowledging that executable scripts are just another
       media type).

       General Information Services

       There are many other possible uses of multimedia data in networked
       information servers which don't conveniently fall into any of the
       above categories. Some examples are given below.

          o    On-line documentation.  Manuals and instruction books often
               rely heavily on pictorial information, and are enhanced by
               dynamic media types (sound, video).  The ability to access
               centrally-held manuals across a network makes it much easier
               to keep the information up-to-date.

          o    Campus-wide information systems (CWIS) are an important
               growth area.  The opportunities for enhancing such a
               service with multimedia data (e.g., maps) is obvious.

          o    Multimedia news bulletins (e.g., the Internet Talk Radio,
               which is sound only).

          o    Product information (the multimedia equivalent of paper
               advertising matter).

          o    Consumer systems - e.g., tourist information servers.  The
               utility of such systems in an academic/research environment
               is perhaps questionable, but it is likely that such systems
               will address problems which will also be met in this
               environment.  We should be prepared to learn from such
               projects.

    2.2. Data Characteristics

       Some of the characteristics which make data more appropriate for
       network publication rather than publication on physical media are
       listed below.

          o    The data may change frequently.

          o    Implementing corrections and improvements to the data is
               very much easier.

          o    It is more readily available to the data user - no
               purchase/delivery cycle need exist.

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          o    Publication on physical media may not be cost-effective for
               very large volumes of data.  (Of course, there is a cost in
               networking the data as well, but the research/academic user
               is normally insulated from this.)

          o    Access for large user communities can be established without
               requiring each user to purchase a potentially expensive
               physical media peripheral (such as a laser disk player).
               This is particularly helpful in classroom situations.

          o    It may require less effort from the data publisher to make
               data available over a network, rather than set up a manual
               mechanism for distributing physical media.

          o    If related data from many different sources is to be
               published, it may be more efficient to leave the data in
               situ, and simply publish the network addresses of the data.

       There are counter-reasons which may make physical media distribution
       more appropriate:

          o    Easier to charge for.  (However, charging mechanisms do
               exist in some network information systems.  It may be that
               potential information providers need to be made more aware
               of this.)

          o    Easier to deter or prevent copyright infringement, using
               traditional copy-protection techniques.

    2.3. Requirements Definition

       From studying the applications described in the preceding section,
       and from discussions with the people involved with the applications,
       it is possible to draw up a list of general requirements which a
       distributed multimedia information system for the academic and
       research community should satisfy.  These requirements are informally
       described in the following subsections.  The descriptions are
       necessarily informal and incomplete: every individual application
       will have its own detailed requirements, which would take a great
       deal of effort to determine (and indeed some of the requirements may
       not become apparent until the application is into its development
       phase).

       Platforms

       It is clear that the European academic community, in common with
       other such communities, requires support for three main platforms:
       UNIX, Apple Macintosh, and PC/Windows.  For multimedia client/server

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       systems, the latter two are less appropriate as server platforms, but
       client support for all three is vital.  UNIX will be most often used
       as the server platform.

       There are other systems, such as VAX/VMS, which are also important in
       some sectors.

       Media Types

       Unsurprisingly, all applications require text data to be supported as
       a basic media type.  Image and graphic media types are next in
       importance, followed by "application-specific" data (such as tabular
       scientific data, mathematical equations, chemical data types, etc).
       Sound and video media types are becoming more important as users
       discover how these can enhance applications.

       Many different encodings are possible for each media type (e.g.,
       image data can be encoded as TIFF, PCX, GIF, PICT and many more).  An
       information system should not constrain the type of encoding used,
       and should ideally offer either a range of alternative encodings, or
       conversion facilities between the stored encoding and an encoding
       suitable for display by the client workstation.

       Hyperlinks

       It is clear that many applications require their users to be able to
       navigate through the information base according to relationships
       determined by the information provider - in other words, hyperlinks.
       Academic publishing, CAL, on-line documentation and CWIS systems all
       require this capability.  The user should be able, by some action
       such as clicking on a highlighted word in a text node or on a button,
       to cause another node or nodes to be retrieved and displayed.

       Some "hypermedia" systems are in fact simply hypertext, in that they
       require the source anchor of a hyperlink to be in a text node.  A
       true hypermedia system allows hyperlinks to have their source anchors
       in nodes of any media type.  This allows a user to click the mouse on
       a component of a diagram or on part of a video sequence to cause one
       or more related nodes to be retrieved and displayed.

       Some hypermedia systems allow target anchors of a hyperlinks to be
       finer-grained than a whole node - e.g., the target anchor could be a
       word or a paragraph within a text document.  Without such a
       capability, it is necessary for target nodes to be quite small if
       precision is required in a hyperlink.  This may be difficult to
       manage, and fine-grained target anchors are therefore better.

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       Additional structure above or orthogonal to the underlying
       hyperlinked data is required in some applications.  This allows the
       same (generally non-textual) data to be used in several different
       applications, or the implementation of different access paradigms.

       Presentation

       Related information of different media types must be capable of
       synchronised display.  Commercial multimedia authoring packages
       provide many different ways of presenting, synchronising and
       interacting with media elements.  Some of these are summarised below.

          o    Backdrops.  An application may present all its visual
               information against a single background bitmap - e.g.,
               a CAL application might use a background image of an open
               textbook, with graphics, text and video data all presented
               on the open pages of the book.

          o    Buttons.  A "button" can be defined as an explicitly-
               delimited area of the display, within which a mouse click
               will cause an action to occur.  Typically, the action will
               be (or can be modelled as) a hyperlink traversal.
               Applications use different styles of button - some may use
               "tabs" as in a notebook, or perhaps "bookmarks" in
               conjunction with the open textbook backdrop mentioned above.
               Others may use plain buttons in a style conforming to the
               conventions of the host platform, or may simply highlight a
               word or phrase in a text display to indicate it is "active".

          o    Synchronisation in space.  When two or more nodes are
               presented together (e.g., because a link with more than one
               target anchor has been traversed), the author of the
               hyperdocument may wish to specify that they be presented in
               a spatially-related way.  This may involve: x/y
               synchronisation - e.g., a video node being displayed
               immediately above its text caption; it may involve
               contextual synchronisation - e.g., an image being displayed in
               a specific location within a text node; or it may involve z-
               axis synchronisation as well - for instance a text node
               containing a simple title being displayed on top of an
               image, with the text background being transparent so that
               the image shows through.

          o    Synchronisation in time.  Isochronous data may require
               synchronisation - the obvious case being audio and video
               tracks (where these are held separately).  Other examples
               are: the synchronisation of an automatically-scrolling text
               panel to a video clip (for subtitling); or to an audio clip

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               (e.g., a translation); or synchronising an animation to an
               explanatory audio track.

       Searching

       Database-type applications require varying degrees of sophistication
       in retrieval techniques.  For applications addressed in this report,
       non-text nodes form the major data of interest.  Such nodes have
       associated descriptions, which may be plain text, or may be
       structured into fields.  Users need to be able to search the
       descriptions, obtain a list of "hits", and select nodes from that
       list to display.  Searching requirements vary from simple keyword
       searching, via full-text indexing (with or without Boolean
       combinations of search words), to full SQL-style database retrieval
       languages.

       Interaction

       The user must be able to annotate documents retrieved from the
       information server.  The annotations may be stored locally.
       Similarly, the user may wish to add his own (locally-held) hyperlinks
       to documents.  (Actual modification of documents in the information
       system itself, or shared annotations to documents - i.e., the
       information system as a CSCW environment - is viewed as separate
       issue which this report does not address.)

       If an information provider has included contact details (such as a
       mail address) in a document, it should be possible for the reader to
       invoke a program (such as a mailer) which initiates communication
       with the author.

       In some applications, it may make sense for a user to be able to
       specify a region of interest in an image or movie clip, and to
       request a more detailed view of (or other information about) that
       region.

       Some applications require a sequence of images to be presented under
       control of the user.  For instance, a three-dimensional microscopic
       structure could be represented as a sequence of images taken with the
       microscope focused on a different plane for each image.  For display,
       the user could control which image was displayed using some kind of
       slider control, giving the illusion of focusing a microscope.  (This
       particular example has been taken from the Theseus project at John
       Moore's University, Liverpool, GB.)

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       Quality of Service

       Research has shown [3] that user toleration of delay in computer
       systems depends on user perception of the nature of the requested
       action.  If the user believes that no computation is required,
       tolerable delays are of the order of 0.2s.  If the user believes the
       action he or she has requested the computer to perform is "difficult"
       - for instance a computation of some form - then a tolerable delay is
       of the order of 2s.  Users tend to give up waiting for a response
       after about 20s.  Networked multimedia information systems must be
       able to provide this level of responsiveness.

       Management

       In order to support applications involving real-money information
       services (e.g., academic publishing) and learning/assessment
       applications, there must be a reliable and secure access control
       mechanism.  A simple password is unlikely to suffice - Kerberos
       authentication procedures are a possibility.

       Users must be able to determine the charge for an item before
       retrieving it (assuming that pay-per-item will be a common paradigm
       alternatives such as pay-per-call, pay-per-duration are also
       possible).  Access records must be kept by the information server for
       charging purposes.

       Learning applications have similar requirements, except that the
       purpose here is not to charge for information retrieved, but to
       monitor and perhaps assess a student's progress.

       Scripting

       Many authoring packages provide scripting languages.  In most cases,
       these languages are used to manage the presentation environment and
       control navigation within the hypermedia document.  There are other,
       declarative rather than procedural, methods for achieving this, so
       scripting of this type is not necessarily a requirement.  However,
       some application areas require executable scripts for other purposes
       (e.g., simulations in CAL applications).  Care in providing such a
       facility is required, because of the potential for abuse (the
       possibility of "trojan" scripts).  However, there is work going on to
       produce "safe" scripting languages - an example is "safe tcl", being
       developed by Borenstein and Ousterhout (contact
       ouster@cs.berkeley.edu).

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       Bytestream Format

       For the easy transfer and handling of a hyperdocument, it must be
       capable of being encoded into a bytestream form, in such a way that
       the structure of the document is preserved and it can be decoded
       without loss of information.

       This facility makes it possible for such documents to be supplied to
       a user over electronic mail, in such a way that he or she can browse
       them at his or her own site.  This may be appropriate where the user
       does not have a direct connection to the Internet.  It will also be
       useful for printing the hyperdocument.

       Authoring

       It is essential that a multimedia information system should have
       adequate authoring tools which make it easy to prepare and publish
       hypermedia information.  Such tools need similar power to existing
       commercial multimedia authoring software for stand-alone multimedia
       applications.

    3. Existing Systems

       This chapter describes some existing distributed information systems
       in sufficient detail to reveal how they handle multimedia data, and
       analyses how well they meet the requirements outlined in the
       preceding chapter.

    3.1. Gopher

       The Internet Gopher is a distributed document delivery service.  It
       allows a neophyte user to access various types of data residing on
       multiple hosts in a seamless fashion.  This is accomplished by
       presenting the user with a hierarchical arrangement of nodes and by
       using a client-server communications model.  The Gopher server
       accepts simple queries, and responds by sending the client a node
       (usually called a document in this context).

       Client software is available for a large number of systems,
       including:

            o UNIX (character terminals)

            o X windows

            o Apple Macintosh

            o MS DOS

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            o NeXT

            o VM/CMS

            o VMS

            o OS/2

            o MVS/XA

       Servers are available for systems such as:

            o UNIX

            o VMS

            o Apple Macintosh

            o VM/CMS

            o MVS

            o MS DOS

       Gopher was developed at the University of Minnesota.

       Gopher User Image

       A Gopher client offers an interface into "gopherspace", which appears
       to the user as a hierarchy of menus and document nodes, similar in
       some ways to a file system hierarchy of directories and files.
       Selecting an entry from a menu node causes a further menu to appear,
       or causes a document to be retrieved and displayed.

       As well as "ordinary" document nodes, Gopher has "search nodes" when
       one of these is selected from a menu, the user is prompted for one or
       more words to search on.  The result of the search is a "virtual"
       menu, containing entries for document nodes (within some subset of
       gopherspace) which match the search.  A special type of Gopher search
       server called "veronica" provides access to a database of all
       directory nodes in gopherspace.  This allows a user to construct a
       virtual menu of all Gopher menu items containing a particular word.
       WAIS databases may also be located at Gopher search nodes, since some
       Gopher servers understand the format of WAIS index files.

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       Gopher Protocol

       Gopher uses a client-server paradigm.  The Gopher protocol runs over
       a reliable data stream service, typically TCP, and is fully defined
       in RFC 1436.  The following paragraphs give an overview which is
       sufficient for understanding how multimedia data is handled in
       Gopher.

       A Gopher client opens a TCP connection to a Gopher server (defined by
       machine name and TCP port number), and sends a line of text known as
       the "selector" to request information from the server.  The server
       responds with a block of data, and then closes the connection.  No
       state is retained by the server.  A null (empty) selector tells the
       Gopher server to return its "root" menu node, containing pointers to
       other information in gopherspace.

       A menu is returned from a Gopher server as a sequence of lines of
       text, each corresponding to one entry in the menu.  Each line (which
       is sometimes called a "Gopher reference") contains the following
       data, which can be used by the client software to retrieve and
       display the corresponding node in gopherspace.

          o    A single character which identifies the type of the node.
               Possible values of this type ID are given below.

          o    A human-readable string which is used by the client software
               when it displays the menu entry to the user.

          o    The selector which should be used by client software to
               retrieve the node.  It is treated as opaque by the client
               software.

          o    The domain name of the host on which the node is held.

          o    The port number to use for the TCP connection.

       A document node is sent by a Gopher server simply as lines of text
       terminated by a dot on a line by itself, or as raw binary data, with
       the end of the data indicated by the server closing the TCP
       connection.  The choice depends on the type of node.

       The currently-defined type IDs are as follows:

            0       Node is a file.

            1       Node is a directory.

            2       Node is a CSO phone book server.

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            3       Error.

            4       Node is a BinHexed Macintosh file.

            5       Node is DOS binary archive of some sort.

            6       Node is a UNIX uuencoded file.

            7       Node is a search server.

            8       Node points to a text-based telnet session.

            9       Node is a binary file.

            T       Node points to a TN3270 connection.

       Some experimental IDs are also in use:

            s       Node contains -law sound data.

            g       Node contains GIF data.

            M       Node contains MIME data.

            h       Node contains HTML data.

            I       Node contains image data of some kind.

            i       In-line text type.

       The process for defining new data types and corresponding IDs is not
       clear.

       Gopher+ Protocol

       The Gopher+ protocol is an extension of the Gopher protocol.  Gopher+
       is defined informally in [4].  It is designed to be downwards
       compatible with the original protocol, so that old Gopher clients may
       access Gopher+ servers (without being able to take advantage of the
       new facilities), and Gopher+ clients may access old Gopher servers.
       Gopher+ is still at the experimental stage, and is liable to change.

       The most important new feature is the introduction of "attributes"
       associated with individual nodes.  The client may retrieve the
       attributes of a node instead of the node contents.  Attributes
       defined so far include:

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        INFO               Contains the Gopher reference of the node.
                           Mandatory.

        ADMIN              Contains administrative information, including
                           the mail address of the server administrator and
                           the last-modified date of the node.  Mandatory.

        VIEWS              Contains a list of one or more "view
                           descriptors", each of which describes an
                           alternate view of the node.  For instance, an
                           image node may contain a TIFF view, a GIF view,
                           a JPEG view, etc.  The client software (or the
                           user) may choose which view to retrieve.  The
                           size of the view is also (optionally) available
                           in this attribute.  The Gopher+ Attribute
                           Registry (see below) defines the permitted view
                           types.

        ABSTRACT           This attribute contains a short description of
                           the item.  It may also include a Gopher
                           reference to a longer abstract, held in a
                           separate Gopher node.

        ASK                This attribute is used for the interactive query
                           extension. The interactive query facility in
                           Gopher+ is used to obtain information from a
                           user before retrieving the contents of a node.
                           The client fetches the ASK attribute, which
                           contains a list of questions for the user. His
                           or her responses to those questions are sent
                           along with the selector to the server, which
                           then returns the contents of the node.  This
                           facility could be used as a very simple way of
                           querying a database, for instance.  Using the
                           interactive query facility to supply a password
                           for access control purposes is not a good idea -
                           there are too many opportunities for
                           masquerading.

       The University of Minnesota maintains a registry of Gopher+ attribute
       types.  For the VIEWS attribute, the registry contains a list of
       permitted view types.  Note that these view types have a similar
       function to the type identifier described in the preceding section.

       The general format of a Gopher+ view descriptor is:

          xxx/yyy zzz: <nnnK>

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       where xxx is a general type-of-information advisory, yyy is what
       information format you need understand to interpret this information,
       zzz is a language advisory (coded using POSIX definitions), and nnn
       is the approximate size in bytes.  Possible values for xxx include
       text, file, image, audio, video, terminal.

       (It now appears that the University of Minnesota Gopher Team accepts
       the need to be consistent in the use of type/encoding attributes with
       the MIME specification.  The Gopher+ Type Registry may thus
       eventually disappear, together with the set of xxx/yyy values it
       currently contains.)

       No view descriptors for directory nodes are currently registered.

       In order to make use of the information available in attributes, it
       is necessary to fetch the attributes before fetching the contents of
       a node.  Gopher+ provides a way of fetching the attributes for each
       entry in a menu at the same time as the menu is retrieved.  This
       saves having to establish two successive TCP connections to fetch a
       single document, at the expense of some additional client software
       complexity.

       Gopher Publishing

       The procedure for making data available using the Unix Gopher server
       "gopherd" is very straightforward.  The hierarchical nature of the
       Unix file system closely matches the Gopher concept of menus and
       documents.  The gopherd program exploits this - Unix directories are
       represented as Gopher menu nodes, and Unix files as Gopher document
       nodes.  The names of directories and files are the entries in Gopher
       menus.  This can lead to awkward file names containing spaces, so
       gopherd provides an aliasing mechanism (the \.cap directory) to get
       round this.

       To represent menu entries pointing to Gopher nodes on other servers,
       special "link" files (starting with a dot) are used.

       The type ID for a document node is determined from the extension of
       its Unix filename.  If a client requests a file containing a shell
       script, the script is executed and the output returned to the client.

       The Gopher+ version of gopherd is similar, but the .cap directory is
       replaced by a configuration file gopherd.conf.  This file is used to
       specify administration attributes, and the mapping between filename
       extensions and view descriptors.  Some limited access control (based
       on the client's IP address/domain name) is also provided by the
       Gopher+ version of gopherd.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       Published Non-text Data

       There is already some useful non-text data published on Gopher almost
       exclusively image data.  See for example the Vatican Library
       Exhibition at the University of Virginia Library, the ArchiGopher at
       the University of Michigan, the weather machine at the University of
       Illinois.  Some of these are described in the User Requirements
       chapter of this report.

       There seem to be rather fewer sound archives in gopherspace, but
       interested users may access the Edinburgh University Computing
       Service Gopher server on gopher.ed.ac.uk, where the Testing Area
       contains 20 or 30 short audio files in Sun audio format.  Note - the
       availability of this archive is not guaranteed.

       Advantages

       The main factor in favour of Gopher is its widespread penetration.
       There are over 1000 Gopher servers world-wide.  This popularity is
       due in part to the ease of setting up a Gopher server and making
       information available on it, particularly on a Unix platform.

       Limitations

       It is unfortunate that the relatively well-defined MIME types were
       not adopted in Gopher+.  As mentioned above, this may yet happen,
       although there appear to be reasons for keeping the set of MIME types
       small whereas Gopher requires a wide range of types to offer to
       clients.  The latest word is that the MIME registry will be expanded
       to include the types which the Gopher+ developers want.

       Gopher is inflexibly hierarchical in nature.  Hypertext or hypermedia
       it is not - links to other nodes from within document nodes are not
       possible.  There is a suggestion in the Gopher+ specification that
       alternate views of directory nodes could be used to provide some kind
       of hypermedia capability, but this does not yet exist, and it is
       unlikely that it could be made to work as easily as the WWW hypertext
       model.

       There is no access control at the user level - anyone can retrieve
       anything on a Gopher server.  There is no provision for charging for
       information.

    3.2. Wide Area Information Server

       The Wide Area Information Server (WAIS) system allows users to search
       for and retrieve information from databases anywhere on the Internet.
       WAIS uses a client-server paradigm, and client and server software is

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    RFC 1614        Network Access to Multimedia Information        May 1994

       available for a wide range of platforms.  Client applications are
       able to retrieve text or other media documents stored on the servers,
       by specifying keywords.  The server software searches a full-text
       index of the documents, and returns a list of documents containing
       the keywords (ranked according to a heuristic algorithm).  The client
       may then request the server to send a copy of any of the documents
       found.  Relevant documents can be fed back to a server to refine the
       search.  Successful searches can be automatically re-run, to alert
       the user when new information becomes available.

       WAIS was developed by Thinking Machines Corporation of Cambridge,
       Massachusetts, in collaboration with Apple Computer Inc., Dow Jones
       and company, and KPMG Peat Marwick.  The WAIS software has been made
       freely available; however Thinking Machines has announced that they
       will stop support for their publicly-distributed WAIS as of version
       8b5.1.  Future support and development of the publicly-distributed
       WAIS has been taken over by CNIDR (Clearinghouse for Networked
       Information Discovery and Retrieval) in the USA.  Future CNIDR
       releases will be called FreeWAIS.  A new company, WAIS Inc, has been
       formed by Thinking Machines to take over commercial exploitation of
       the Thinking Machines WAIS software.

       WAIS server software is available for the following platforms:

            o       UNIX

            o       VAX/VMS

       Client software is available for the following platforms:

            o       UNIX (versions for X, Motif, Open Look, Sun View)

            o       NeXT

            o       Macintosh

            o       MS DOS

            o       MS Windows

            o       VAX/VMS

       There are currently over 400 WAIS databases available on the
       Internet.  WAIS is also the basis of some commercial information
       services on private networks.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       WAIS User Image

       In order to ask a question, the user must first select one or more
       databases in which to look for the answer.  (The list of all
       available databases is available from a number of well-known sites.)
       The next step is to enter one or more keywords as the basis of the
       search.  The search will return a list of documents (the "result
       set") which contain any of the keywords.  Each document is given a
       ranking (a number between 1 and 1000) which indicates how relevant to
       the user's question the server believes the document to be.  The size
       of each document is also shown in the list.  The user may limit the
       size of the result set - the default limit is typically 40 documents.

       The user may then choose to retrieve and display one or more
       documents from the list.  Alternatively, he or she may designate one
       or more documents in the list as "relevant", and perform another
       search to find "more documents like this".  This is called "relevance
       feedback".

       The user may retrieve general information about the database, and may
       examine the catalogue of all documents in the database.  There is
       also a "database of databases", which may be searched to identify
       WAIS databases which may be relevant to a subject.

       WAIS Protocol

       The user interface (client) talks to the server using an extended
       version of a standard ANSI protocol called Z39.50.  This is now
       aligned with the ISO SR (Search and Retrieval) protocol for
       bibliographic (library) applications, which is part of OSI.  The
       present WAIS protocol does not utilise a full OSI stack - APDUs are
       transferred directly over a TCP/IP connection.  The WAIS protocol is
       described in [5].

       WAIS does not, at this time, implement the full Z39.50-1992
       specification - in particular, WAIS does not permit Boolean searches
       (e.g., "find all documents containing 'chalk' and 'cheese' but not
       'green'").  However, Boolean search capability is being added to the
       FreeWAIS implementation.  There are facilities in the Z39.50 protocol
       for access control and charging, but these are not currently
       implemented in WAIS.

       The WAIS extensions to Z39.50 are mainly to provide the relevance
       feedback capability.

       Note that the Z39.50 protocol is not stateless - the result set may
       in some circumstances be retained by the server for the user to
       further refine or refer to.  However, the subset of Z39.50 used by

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       current WAIS implementations mean that server implementations may be
       stateless.

       Document type is determined by the server from information in the
       database index (see below), and is sent to the client as part of the
       result set.

       WAIS Publishing

       The first step in preparing data for publishing in a WAIS database is
       to use the 'waisindex' utility.  This takes a set of text files, and
       produces an index file which contains an occurrence list of words of
       three or more letters in every file.  This index file is used by the
       WAIS server software to resolve search requests from clients.

       The 'waisindex' utility indexes files in a wide range of text
       formats, as well as postscript and image files in various encodings
       (only the file name is indexed for image files).  Some of the text
       formats involve a file as being treated as a collection of documents
       for the purposes of WAIS access.  Note that there appears to be no
       formal "registry of types" - just whatever the waisindex program
       supports.  There is no distinction between media type and encoding
       format.

       Published Non-text Data

       There is relatively little non-text data available in WAIS databases.

          o    URL=wais://quake.think.com:210/CM-images is a database of
               TIFF images from the Connection Machine.

          o    URL=wais://mpcc3.rpms.ac.uk:210/home/images/pathology/RPMS-
               pathology is a database of histo-pathological images and
               documentation on mammalian endocrine tissue.

          o    URL=wais://starhawk.jpl.nasa.gov:210/pio contains GIF images
               from NASA planetary probe missions, together with their
               captions.  The presence of the caption index information
               makes it difficult to construct a search which returns
               images in the result set increasing the maximum result set
               size may help.

       Advantages

       WAIS is ideally suited for its intended purpose of searching
       databases of textual information on the basis of keywords.  It
       appears to have the potential to satisfy the requirements of some of
       the "database" category of applications mentioned in Chapter 1.

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       Limitations

       WAIS is not (and does not pretend to be) a general-purpose
       information system, as Gopher and WWW are.  WAIS does not have
       hyperlinking, and offers a purely flat structure.

       A limitation which is particularly apparent is the way that the
       current version of FreeWAIS indexes non-text files - using only the
       filename!  However, it does seem that simply changing the indexing
       program to allow a list of keywords to be attached to non-text files
       would suffice to allow sensible indexing of non-text data.  The
       commercial (WAIS Inc) version of WAIS allows several files to be
       associated together for indexing and retrieval purposes.
       Furthermode, the UCSF Centre for Knowlege Management is modifying the
       FreeWAIS code to support the indexing of multiple content types.  The
       document returned by WAIS will be an HTML document containing
       pointers to the multimedia data.  Contact dcmartin@library.ucsf.edu
       for further information.

       WAIS is not a fully-featured query/response protocol such as SQL.  It
       has no concept of fields, or numeric data types.

       It appears to be impossible to retrieve a document from its catalogue
       entry in many of the existing databases.

    3.3. World-Wide Web

       The World-Wide Web project (also known as WWW or W3), started and
       driven by CERN, is a large-scale distributed hypertext system.  It
       uses the standard client-server paradigm, with client "browser"
       software responsible for fetching and displaying data.  Originally
       aimed at the High Energy Physics community, it has spread to other
       areas.

       Browser software is available for a large number of systems
       including:

            o       Line-mode dumb terminal.

            o       Terminal with Curses support

            o       Macintosh

            o       X/Motif

            o       X11

            o       PC/MS Windows

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    RFC 1614        Network Access to Multimedia Information        May 1994

            o       NeXT

       There is server software available for:

            o       VM mainframes.

            o       UNIX

            o       Macintosh

            o       VMS

       WWW User Image

       The WWW world consists of nodes (usually called documents) and links.
       Links are connections between documents: to follow a link, a reader
       clicks with a mouse on a word in the source document, which causes
       the linked-to document to be retrieved and displayed.  (On systems
       without a mouse, the user types a number instead.)

       Indexes are special documents which, rather than being read, may be
       searched.  To search an index, a reader supplies keywords (or other
       search criteria).  The result of a search is a "virtual" document
       containing links to the documents found.  All documents, whether
       real, virtual or indexes, look similar to the reader.

       The WWW addressing mechanism means that an interface to Gopher and
       anonymous FTP information sources may be established, in a way which
       is transparent to the user.  Thus, the whole of gopherspace is part
       of the Web.  Transparent gateways to other systems, including Hyper-G
       and WAIS, are also available.

       URL

       All nodes on the Web are addressed using the "Universal [or Uniform]
       Resource Locator" (URL) syntax, defined in [6].  This is an Internet
       Draft produced by the IETF URL Working Group.

       A URL is a name for an object (which may be a document or an index)
       on the Internet.  It has the general form:

          <scheme> : <path> [ # <anchorid> ]

       The <scheme> identifies an access protocol or method for the object.
       Some of the schemes are HTTP (the native WWW protocol), anonymous
       FTP, Andrew file system, news, WAIS, Gopher.  The <path> component
       locates the document in a way significant for the access method.

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       Thus for instance for anonymous FTP, the path includes the fully
       qualified domain name of the host on which the document resides, and
       the directory and file name under which it may be found.  For some
       schemes, the <path> may include a search string (or combination of
       strings) which is used to address a "virtual" object formed by
       searching an index of some kind.  The HTTP, WAIS and Gopher schemes
       can use search strings, which usually follow the rest of the path,
       separated from it by a ?.

       The optional <anchorid> is used for addressing within an object.  Its
       interpretation is not defined in the URL specification.

       "Partial" URLs may be specified.  These are used within a document on
       the Web to refer to another "nearby" document - for instance to a
       document in another file on the same machine.  Certain parts of the
       URL (e.g., the scheme and machine name) may be omitted, according to
       well-defined rules.  This makes it much easier to move groups of
       documents around, while maintaining the links within and between
       them.

       A URL locates one and only one object on the Internet.  However, more
       than one URL may point to the same object.  Given two URLs, it is not
       in general possible to determine whether they refer to the same
       object.  Furthermore, there is no guarantee that a single URL will
       refer to the same object at different times (the object may change
       incrementally, or it may be completely replaced with something
       different, or it may indeed be removed).

       HTTP

       HTTP (HyperText Transfer Protocol) is the protocol employed between
       server and client.  It is defined in [7].  The protocol is currently
       being revised (see the Future Developments section below), and will
       eventually be proposed as an Internet standard.

       The original protocol is extremely simple, and requires only a
       reliable connection-oriented transport service, typically TCP/IP.

       The client establishes a connection with the server, and sends a
       request containing the word GET, a space, and the partial URL of the
       node to be retrieved, terminated by CR LF.  The server responds with
       the node contents, comprising a text document in the Hypertext Markup
       Language (HTML).  The end of the contents is indicated by the server
       closing the connection.

    Adie                                                           [Page 36]

    RFC 1614        Network Access to Multimedia Information        May 1994

       HTML

       HTML (HyperText Markup Language) is the way in which text documents
       must be structured if they are to contain links to other documents.
       Non-HTML text documents may of course be made available on the Web,
       but they may not contain links to other documents (i.e., they are
       leaf nodes), and they will be displayed by browsers without
       formatting, probably using a fixed-width font.  Like HTTP, HTML is
       also undergoing enhancement, but the original version is defined in
       [7], and is being submitted as an Internet draft.

       HTML is an application of SGML (Standard Generalized Markup
       Language).  It defines a range of useful tags for indicating a node
       title, paragraph boundaries, headings of several different levels,
       highlighting, lists, etc.  Anchors are represented using an <A> tag.

       For instance, here is an example of HTML containing an anchor:

       The HTTP protocol implements the WWW <A NAME=13
       HREF="../../Administration/DataModel.html">data model</A> .

       The location of the anchor is the text "data model".  It is a source
       anchor, with a target given by the URL in the HREF attribute, so the
       text would appear highlighted in some way in a client's window, to
       indicate that clicking on it would cause a hyperlink to be traversed.
       It is also a target anchor, with an anchor ID given by the NAME
       attribute.  A source anchor referring to this target would specify
       #13 at the end of the node's URL.  Traversing a hyperlink to this
       node would cause the entire node to be retrieved, but the target
       anchor text would be displayed in some emphasised way - for instance
       if the retrieved text is displayed in a scrolling window, it might be
       positioned such that the target anchor appears at the top of the
       window.

       Another attribute of the <A> element, TYPE, is also available, which
       is intended to describe the nature of the relationship modelled by
       the link.  However, this is not in extensive use, and there appears
       to be no registry of the possible values of such types.

       Future Developments

       HTTP and HTML are currently being extended in a backward-compatible
       way to add multimedia facilities.  [8] describes the HTTP2 protocol.
       The revised HTML is defined in [9].  Both documents are subject to
       change (and indeed the HTML2 specification has changed substantially
       during the preparation of this report).

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    RFC 1614        Network Access to Multimedia Information        May 1994

       The revised HTML contains many enhancements which are useful for
       multimedia support.  Some of the most relevant are listed below.

          o    "Universal Resource Numbers" are a proposed system for
               unique, timeless identifiers of network-accessible files
               presently being designed by IETF Working Groups.  URNs must
               be distinguished from URLs, which contain information
               sufficient to locate the document. URNs may be allocated to
               nodes and may be represented in source anchors.  This saves
               client software from retrieving a copy of something it
               already has - allowing sensible caching of large video
               clips, for instance.  The disadvantage is that when
               something is changed and given a new URN, the source anchors
               of all links which point to it must be changed (and the URNs
               of these documents must therefore be changed, and so on).
               Therefore, it makes sense to allocate URNs only to very
               large documents which change rarely, and not to the
               documents which reference them.

          o    The title of a destination document may be included as
               anattribute of a source anchor.  This allows a client to
               display the title to the user before or during retrieval,
               and also allows data which does not itself contain a title
               (e.g., image data) to be given one.

          o    There is provision for in-line non-text data (e.g., images,
               video, graphics, mathematical equations), which appears in
               the samewindow as the main textual material in the node.

          o    The concept of the relationship expressed by a hyperlink is
               expanded.  Both source and target anchors may contain
               relation attributes which point forwards and backwards
               respectively. Possible relationships include "is an index
               for", "is a glossary for", "annotates", "is a reply to", "is
               embedded in", "is presented with".  The last two are useful
               for multimedia - for instance, the "embed" relationship
               could cause a retrieved image to be fetched and embedded in
               the display of a text node, and the "present" relationship
               could cause a sound clip to be automatically retrieved and
               presented along with a text node.

       The HTTP2 protocol maintains the same stateless
       connect/request/response/close procedure as the current HTTP
       protocol.  Data is transferred in MIME-shaped messages, allowing all
       MIME data formats (including HTML) to be used.  As well as the GET
       operation, HTTP2 has operations such as:

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    RFC 1614        Network Access to Multimedia Information        May 1994

        HEAD               Fetch attribute information about a node
                           (including the media type and encoding)

        CHECKOUT/CHECKIN/PUT/POST

                           These allow nodes to be checked out for updating
                           and checked back in again, and new nodes to be
                           created.  New node data is supplied in MIME
                           shape with the request.

       The request from the client can contain a list of formats which the
       client is prepared to accept, user identification, authorisation
       information (a placeholder at present), an account name to charge any
       costs to, and identification of the source anchor of the hyperlink
       through which the node was accessed.

       The response from the server may contain a range of useful attributes
       (e.g., date, cost, length - but only for non-text data).  The server
       may redirect the query, indicating a new URL to use instead.  It may
       also refuse the request because of authorisation failure or absence
       of a charge account in the request.

       The protocol also contains a mechanism which is designed to allow the
       server to make an intelligent decision about the most appropriate
       format in which to return data, based on information supplied in the
       request by the client.  This may for instance allow a powerful server
       to store the uncompressed bitmap of an image, but to compress it on
       request using an appropriate encoding, according to the decoding
       capabilities announced by the client.

       An HTTP2 server and client are currently under test.  Some HTML2
       features are already fitted to the XMosaic browser.

       Mosaic

       The Mosaic project, located at the US National Centre for
       Supercomputing Applications (NCSA) at the University of Illinois, is
       developing a networked information system intended for wide-area
       distributed asynchronous collaboration and hypermedia-based
       information discovery and retrieval.  Mosaic, which is specifically
       oriented towards scientific research workers, has adopted the World
       Wide Web as the core of the system, and the first Mosaic software to
       appear was the XMosaic WWW client for UNIX with X.  Other clients of
       similar functionality are under development for the Apple Macintosh
       and the PC with Windows.

       The capabilities of the XMosaic browser include:

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    RFC 1614        Network Access to Multimedia Information        May 1994

          o    Support for NCSA's Data Management Facility (DMF) for
               scientific data.

          o    Support for transferring data with other NCSA tools such
               asCollage, using NCSA's Data Transfer Mechanism (DTM).

          o    The ability to "check out" documents for revision, and to
               check them back in again.

          o    Local and remote annotation of Web documents.

       Future planned functionality includes:

          o    In-line non-text data (in addition to images).

          o    Information space graphical representation and control.

          o    Hypermedia document editing.

          o    Information filtering.

       NCSA intends to make the entire Mosaic system publicly available and
       distributable.

       The XMosaic browser was used extensively for finding and retrieving
       information used to prepare this report.

       Web Publishing

       Making a web is as simple as writing a few SGML files which point to
       your existing data. Making it public involves running the FTP or HTTP
       daemon, and making at least one link into your web from another. In
       fact,  any file available by anonymous FTP can be immediately linked
       into a web. The very small start-up effort is designed to allow small
       contributions.

       At the other end of the scale, large information providers may
       provide an HTTP server with full text or keyword indexing. This may
       allow access to a large existing database without changing the way
       that database is managed. Such gateways have already been made into
       Digital's VMS/Help, Technical University of Graz's "Hyper-G", and
       Thinking Machine's WAIS systems.

       There are a few editors which understand HTML - for instance on UNIX
       and on the NeXT platform.

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       Published non-text data

       See the multimedia demo node on:

       http://hoohoo.ncsa.uiuc.edu:80/mosaic-docs/multimedia.html

       This contains links to images, sound, movies and postscript media
       types.  The media type is determined by the filename extension in the
       URL specification of the target node.  The (XMosaic) client uses this
       to invoke a separate program appropriate for displaying the media
       type, or in some cases it can be displayed embedded within the source
       document.  The latter method uses an <IMG> tag, which is part of
       HTML2.

       Advantages

       WWW is a hypertext system and its underlying technology is thus
       richer than Gopher.  The use of SGML, which is of increasing
       importance in hypermedia systems, allows a great deal of
       expressiveness and structure, and enables text to be presented in an
       attractive way.  The facilities for multimedia data in the extended
       versions of HTTP and HTML are excellent.  It also seems that QOS and
       management issues identified in Chapter 2 are to some degree catered
       for in these extensions.

       Limitations

       There is no indication in the source anchor of the media type of the
       destination node, or of its size (this has been ruled out on the
       argument that the information is likely to degrade with time).  It is
       necessary to perform a HEAD request (in HTTP2) to deduce this.

       Link source anchors must be in text documents, so non-text nodes must
       be leaf nodes.  However, with HTML2 using the <IMG> tag, an embedded
       bitmap may be used as a source anchor, and the position of the mouse
       click within the image is passed to the server, which can then choose
       to return a different document depending on where in the image the
       mouse was clicked.

       WWW is much less prevalent than Gopher, partly because of an
       (erroneous?) perception that setting up an HTTP server is more
       complex than setting up a Gopher server.  There are only about 60
       servers world-wide; however the growth in the use of WWW is much
       faster than the growth in the use of Gopher.  The availability of
       sophisticated WWW clients such as XMosaic is fuelling this growth.

    Adie                                                           [Page 41]

    RFC 1614        Network Access to Multimedia Information        May 1994

    3.4. Evaluating Existing Tools

       This section compares the capabilities of the Gopher, WAIS and
       WorldWide Web systems (abbreviated as GWW) to the informal
       requirements defined in section 2.3.

       Platforms

       The table below gives the names of the most important client software
       for each of GWW on the three most important platforms of interest.
       WWW is the weakest, with clients for the Macintosh and the PC still
       under development.  The main PC Gopher client is "PC Gopher III",
       which is a DOS program, not a Windows program.

        CLIENTS      Gopher          WAIS                WWW

        Macintosh    TurboGopher     WAIStation          (No name)
                                                         (beta version
                                                         available)

        PC with      HGopher (two    WAIS for            Cello (beta
        Windows      others also     Windows, WAIS       version
                     available)      Manager             available),
                                                         Mosaic (beta due
                                                         3Q93)

        UNIX with X  Xgopher,        XWAIS               XMosaic
                     XMosaic

       At present, multimedia support in most of these clients (where it
       exists) is limited to the invocation of external "viewer" programs
       for particular media types.  The exception is XMosaic, which supports
       in-line images in WWW documents.

       Media Types

       The GWW tools can all handle multiple media types well.

          o    Text is very well supported by all three tools.  WWW offers
               facilities for displaying "richer" text, supporting
               headings, lists, emphasised text etc., in a standardised way.

          o    Image data is also well supported, using either external
               viewers (e.g., the TurboGopher client software on a Macintosh
               might invoke the JPEGView program to display an image); or
               in-line display within a text document (WWW with XMosaic on
               UNIX).

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    RFC 1614        Network Access to Multimedia Information        May 1994

          o    There is little direct support for application-specific
               data, but most systems allow data of a nominated type to be
               passed to an external viewer or editor program.  This tends
               to be a function of the client software rather than being
               built in to the protocol or server.  There has been
               discussion in the WWW community about using TeX for
               representing mathematical equations, and about providing
               "panels" within a text document where a separate application
               could render its application-specific data (or indeed any
               data which can be represented spatially).  This latter
               suggestion fits well with the OLE (Object Linking and
               Embedding) approach used in Microsoft Windows.

          o    Sound can be supported through the external "viewer"
               concept. Some platforms don't have readily-available
               "viewers" with "tape recorder"-style controls for replaying.
               There is no single commonly-accepted sound encoding format.

          o    Video data can be handled using external viewers.  MPEG and
               QuickTime are the most common encodings.

       One essential capability of a client/server protocol is the ability
       for the client to determine the type of a node (and a list of
       available encodings) before downloading it.  WAIS and Gopher transfer
       this information in the result set and menu respectively.  WWW
       clients currently determine this information either from analysing
       the URL of a target node, or by the occurrence of the <IMG> tag.  The
       new WWW HTTP2 protocol allows the media type and encoding of a node
       to be determined through a separate interaction with the server.

       The GWW systems all use different methods for expressing type and
       encoding.  WAIS does not distinguish the encoding from the media
       type.  WWW is moving to the MIME type/encoding system.  Gopher does
       not distinguish type and encoding, but Gopher+ does, and is also
       moving to the MIME type/encoding system.

       Hyperlinks

       Only the WWW system has hyperlinks.  Source anchors may be text,
       images, or points within an image.  Target anchors may be entire
       nodes of any media type, or points within (with HTTP2, portions of)
       text nodes.

       Gopher+ could potentially be enhanced to include hyperlinks, but
       there seems to be no development effort going towards this - those
       who need hyperlinking are using WWW.

    Adie                                                           [Page 43]

    RFC 1614        Network Access to Multimedia Information        May 1994

       Gopher menus can be constructed to allow alternative views of
       gopherspace.  For instance, a geographically-organised menu tree of
       gopherspace is in place, but a parallel subject-based menu tree could
       be added as an alternative way of access to the same data.  (There
       are in fact moves to set this up.)  Since WWW offers a superset of
       Gopher functionality, these comments also apply to the Web.  In fact,
       the Web already has a rudimentary subject tree.

       In both Gopher and WWW, non-textual data may be used in different
       information structures without having to maintain more than one copy.

       Presentation

       There is little support in GWW for controlling the presentation of
       non-text data.

          o    Backdrops are not supported by GWW.

          o    Buttons are supported in a limited way - typically, a node
               is retrieved by clicking on a highlighted text phrase, or on
               an entry in a list.  In XMosaic, bitmap images can be used
               as buttons. However, there is no support for different
               styles of button.  Client software may have generic
               navigation buttons (e.g., "Back", "Next", "Home") which are
               always available and don't form part of a node.

          o    Synchronisation in space is not supported by GWW, except
               that WWW supports contextual synchronisation of images using
               the <IMG> tag.

          o    Synchronisation in time is not supported by GWW.

       Searching

       WAIS supports keyword searching, and is very well suited for that
       task.  The Gopher+ protocol could potentially support multimedia
       database querying applications through the ASK attribute, but there
       is as yet no server implementation which supports such database
       applications.  In the WWW project, there are ongoing discussions on
       how best to extend HTML to cope with database query applications - an
       <INPUT> tag has been suggested - but no consensus has yet emerged.

       Both Gopher and WWW can make use of WAIS-type keyword searching:
       either by incorporating WAIS code into the server (enabling WAIS
       index files to be searched); or through WAIS gateways, which run
       searches on remote WAIS servers in response to queries from non-WAIS
       clients.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       Interaction

       XMosaic allows users to make text (or on some platforms, audio)
       annotations to any text node.  The annotations appear at the end of
       the text display..  They are held locally - other users of the node
       do not see the annotations (but a recently added facility allows
       globally-visible annotations held on an "annotation server").  Text
       annotations may include hyperlinks to other nodes (provided the user
       knows how to use HTML).  Other clients do not provide such
       facilities.

       There is a move to add an "email" address notation to URL.  This
       would allow WWW client software to invoke a mail program when a user
       selects an anchor with such a URL.

       There are plans to allow WWW users to delineate a rectangular area of
       interest within an image for use in an HTTP request.

       There is no support in GWW clients for interacting with sequences of
       images in the way described in section 2.3.6.

       Quality of Service

       The user expectations for responsiveness mentioned in section 2.3.7
       are difficult to meet with currently-deployed wide-area network (or
       even LAN) technology, particularly for voluminous multimedia data.
       None of the GWW systems currently exploit the emerging isochronous
       data transfer capabilities of protocols such as RTP and technologies
       such as ATM.  None of them make serious attempts to alleviate the
       problem in other ways (except for WWW, which defines some mechanisms
       in HTTP2 for format negotiation based on size and available bandwidth
       considerations).

       Management

       The following table shows the support for three key management
       facilities in the GWW systems.  The first two facilities require
       support in the client/server protocol, the third requires support in
       the server, but depends on authentication being available.

                            Gopher         WAIS          WWW

        Access control      No             No1           Yes, in
        and                                              HTTP2
        authentication

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        Charging support    No             No            Yes, in
                                                         HTTP2

        Monitoring for      No             No            No
        statistical and
        assessment
        purposes

       Note:

       1. "Access-control-facility" is a feature of Z39.50 which is not used
       by the current WAIS implementations.

       Scripting Requirements

       None of the GWW systems have facilities for the execution of scripts
       by the client, because of security issues (it would be too easy for a
       malicious "trojan" script to be executed).  Gopher and WWW servers
       have the ability for a UNIX script to be run by the server, with the
       script output returned to the client.  Scripting as understood in the
       context of stand-alone multimedia applications does not exist in GWW.

       Bytestream Format

       None of the three GWW systems use a bytestream format for
       interchanging collections of material.  There has been some talk
       about setting up a system akin to the "Trickle" mail server, for
       retrieving single document nodes from GWW using mail.  Such a system
       has been implemented for WWW.

       Authoring tools

       Gopher is sufficiently simple to set up that no special authoring
       tools are required.  WAIS requires only an indexing program (as
       discussed in section 3.2) for preparing material for publication.

       WWW, because it uses a sophisticated authoring language (HTML),
       benefits from the availability of authoring tools.  There are HTML
       editors for UNIX (using the tk toolkit) and the NeXT system.  There
       are no authoring tools designed specifically for exploiting the
       multimedia capabilities of WWW, mainly because these capabilities are
       still evolving.

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    RFC 1614        Network Access to Multimedia Information        May 1994

    4. Research

       This section describes some current research projects in the area of
       distributed hypermedia information systems.

    4.1. Hyper-G

       Hyper-G [10] is an ambitious distributed hypermedia research project
       at a number of institutes of the IIG (Institutes for Information-
       Processing Graz), the Computing and Information Services Centre of
       the Graz University of Technology, and the Austrian Computer Society.
       It is funded by the Austrian Ministry of Science. It combines
       concepts of hypermedia, information retrieval systems and
       documentation systems with aspects of communication and
       collaboration, and computer-supported teaching and learning.

       Unlike WWW, Hyper-G supports bi-directional links.  This enables
       users to see which other documents reference the one they are using,
       and also allows the system to avoid dangling pointers when a linkedto
       document is deleted.  Another difference from WWW is that links are
       kept separately from their source and target nodes, to allow easy
       linking of read-only documents and for ease of link maintenance.  In
       addition to manually defined links, Hyper-G supports automatic static
       and dynamic (i.e., view-time) generation and maintenance of links.

       Hyper-G has a concept of generic "structures" - an additional layer
       of relationships imposed on (and orthogonal to) the web of documents
       and links.  A document can be part of more than one structure, and
       structures may be hierarchically related.  Types of structure
       include:

          o    "Clusters" are a set of documents which are all
               presentedtogether.

          o    "Collections" are unordered sets of documents or other
               structures, and can be used as query domains or to construct
               gopher-like menus.

          o    "Paths" are ordered sets of documents or structures, which
               must be visited sequentially.

       One application of the structure concept is the provision of "guided
       tours" through the information space.

       In addition to hypernavigation, the collection hierarchy and guided
       tours, another strategy for interaction with the system is the use of
       database queries.  Two kinds of query are supported: keyword
       searching in a user-defined list of databases; and collection

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    RFC 1614        Network Access to Multimedia Information        May 1994

       specific form-filling queries.  In the latter case, the answer to the
       query may appear dynamically as the form is filled out.

       Four modes of user identification are supported: "identified", where
       a userid is publicly associated through name and address information
       with a particular individual; "semi-identified", where a userid is
       associated by the system with an individual, but the user is only
       known to other users through a pseudonym; "anonymously identified",
       where the userid is not associated by the system with any individual;
       and "anonymous", where there is no userid (or a generic userid such
       as "guest").  Possible operations in the system depend on the user's
       mode of identification.  Users may access the system in any desired
       mode, and switch to other modes only when necessary.

       Hyper-G contains specific support for multilingual documents and
       document clusters.  Users may specify an ordered list of preferred
       languages, for instance.  There are plans to experiment with
       automatic translation programs.

       Integration of other, external, systems such as WWW into Hyper-G in a
       seamless manner is possible.

       Hyper-G is in use as a CWIS within Graz Technical University.  Client
       software is available for UNIX workstations from DEC, HP, SGI, and
       SUN.  The system is still in an experimental state, but it has been
       used by about 200 students as part of a course on the social impact
       of information technology.

    4.2. Microcosm

       Microcosm [11] is an open hypermedia system developed at the
       University of Southampton.  It is implemented on the PC under MS
       Windows, and versions for the Apple Macintosh and for UNIX with X are
       under development.

       Microcosm consists of a number of autonomous processes which
       communicate with each other by a message-passing system.  Information
       about hyperlinks between documents is stored in a link database, or
       "linkbase", and is not stored in the documents themselves.  This has
       the advantages that:

          o    Links to and from read-only documents (perhaps stored on CD-
               ROM) are possible.

          o    Documents need undergo no conversion process to be imported
               into the system - they can still be viewed and edited using
               the original application which created them, without the
               link information getting in the way.

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          o    It is as easy to establish links to and from non-text
               documents as text documents.

       In Microcosm, the user interacts with a "viewer" program for a
       particular media type.  Such programs may be specifically written for
       use with Microcosm (about 10 such viewers have been written for a
       number of common media types and encodings); or they may be a program
       adapted for use with Microcosm (the programmability of Microsoft Word
       for Windows has allowed it to be so adapted); or it may even be a
       program with no knowledge of Microcosm.

       The user selects an object (e.g., a piece of text) in the viewer, and
       requests Microcosm to perform an action with the object - typically
       to follow a link to another document.  This may involve executing
       another viewer to display the target document.

       Microcosm link source anchors may be specific (denoting a unique
       point in a particular document), local (denoting any occurrence of a
       particular object in a particular document) or generic (denoting any
       occurrence of an object in any document).  Target anchors may specify
       specific objects within a document.  Other link styles are
       textretrieval links (looking up a full-text index , as WAIS does),
       and relevance links to a set of documents using similar vocabulary to
       the source document (again, similar to WAIS's relevance feedback).

       Links may be created by readers as well as by authors.  Dynamically
       computed links may be added to the permanent linkbase for later use.
       A history of link traversal is maintained, and "guided tours" may be
       established through the system which allow the reader to stray from
       and return to the tour.

       Microcosm viewers operate by sending messages to the Microcosm
       system.  In MS Windows, these messages are transferred using DDE
       (Dynamic Data Exchange); in the Apple Macintosh version Apple Events
       are used, and sockets are used on UNIX.  For viewers which are not
       Microcosm aware, the user must transfer the selected object to the
       system clipboard before being able to follow a link from it.

       Networking support in Microcosm is currently under development.
       Components of Microcosm may be distributed to multiple machines there
       is not necessarily a concept of "client" and "server".

       There are problems with the Microcosm approach, common to systems
       which maintain link information separately from documents, and which
       use external viewers.

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          o    Documents move and change, thus invalidating links.
               Microcosm datestamps links to help to detect (but not
               correct) such problems.

          o    It is not always clear what links are available to be
               followed from a document, since the viewer program is
               unaware of the contents of the linkbase.

          o    It is not always possible to indicate the object within a
               document which is the target anchor of a link.  Many viewers
               automatically show the start of the document (e.g., a word
               processor), or perhaps the entire document (e.g., a picture
               viewer).  The user has no way of knowing which part of the
               target document the link just followed points to.

       Microcosm may be viewed as an integrating hypermedia framework - a
       layer on top of a range of existing applications which enables
       relationships between different documents to be established.

       Microcosm is currently being "commercialised".

    4.3. AthenaMuse 2

       AthenaMuse 2 (AM2) is an ambitious distributed hypermedia authoring
       and presentation system under development by the AthenaMuse Software
       Consortium based at MIT.  It is based on the earlier AM1 system
       developed as part of MIT's Project Athena.  The first version of AM2
       is scheduled for January 1994, and will be "pre-commercial software",
       with a fully-commercialised version due about 6 months later.  Both
       the educational and commercial sectors are the intended market.  The
       system will initially be based on X and UNIX workstations, but
       PC/Windows will also be supported in a second phase.  Apple Macintosh
       support has a lower priority.

       The specifications of AM2 are available in [12].  Some of the key
       points are:

          o    AM2 will support import and export of application from and
               tostandard forms.  The project is watching standards such as
               HyTime, MHEG and ODA.

          o    Several "application themes", or frequently-occurring
               collections of functionality, are viewed as useful.  These
               are as follows:

               Application Theme                         Interactive?
               Presentation of multimedia data           No
               Exploration of a rich multimedia          Yes

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               environment
               Simulation of a real-world scenario       Partially
               Communication of real-time                No
               information to the user
               Authoring                                 Yes
               Annotation of material                    Yes

          o    "Interface templates" allow a multimedia application to make
               use of a common format for presenting a range of content.
               This is similar to the "backdrop" concept mentioned in
               section 2.3.4.

          o    A range of link types will be supported.

          o    Media content editors and interface/application editors for
               structuring will be provided.  A third class of editor, the
               "hypermedia notebook", will allow readers to excerpt and
               annotate media from AM2 applications.

       The project is developing multimedia network services, including the
       transmission of digital video, using a client-server paradigm.

    4.4. CEC Research Programmes

       Some of the research programmes sponsored by the Commission for the
       European Community (CEC) contain apparently relevant projects. [1]
       has further details of some of these projects.

       RACE programme

       The RACE programme is outlined in [13], which should be consulted for
       further information about the projects described below.  The RACE
       programme targets the industrial, commercial and domestic sectors,
       and results are not necessarily directly applicable to the research
       and academic community.  RACE project numbers are given.

        RACE Phase I projects, which have mostly completed:

        R1038  MCPR - Multimedia Communication, Processing and
               Representation. This project developed a demonstrator
               multimedia system with communications capability for travel
               agents.

        R1061  DIMPE - Distributed Integrated Multimedia Publishing
               Environment. The project designed and implemented interim
               services for compound document handling, and defined a
               distributed publishing architecture.

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        R1078  European Museums Network. This project aimed to demonstrate
               interactive navigation through a pool of multimedia museum
               objects, using ISDN as the communications network.

        RACE Phase II projects:

        R2008  EuroBridge.

               Aims to demonstrate multi-point multimedia applications
               running over DQDB, FDDI and ATM test networks.

        R2043  RAMA - Remote Access to Museum Archives

               This project follows on from R1078.

        R2060  CIO - Coordination, Implementation and Operation of
               Multimedia Services.

               One aspect of this project is JVTOS - a "Joint Viewing and
               Teleoperation Service".  This aims to integrate standard
               multimedia applications running on a range of heterogeneous
               machines into a cooperative working environment, allowing
               individuals to view and interact with multimedia data on
               colleague's machines.

       ESPRIT Programme

       The ESPRIT research programme is outlined in [14], which should be
       consulted for further information about the projects listed below.
       ESPRIT project numbers are given.

        28     MULTOS - A Multimedia Filing System

               This project, which ran from 1985 to 1990, developed a
               client/server system for filing and retrieval of multimedia
               documents using the ODA interchange format standard (ODIF).

        5252   HYTEA - HyperText Authoring

               This project, which runs from 1991 to 1994, aims to develop
               a set of authoring tools for large and complex hypermedia
               applications.

        5398   SHAPE - Second Generation Hypermedia Application Project

               This project is developing a portable software environment
               comparable to a CASE tool intended to facilitate the
               realisation of complex hypermedia applications.

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        5633   HYTECH - Hypertextual and Hypermedial Technical
               Documentation This project, which ran from 1990-1991, was to
               assess the feasibility of hypermedia technology and to
               devise needed extensions to it in order to support
               applications dealing with technical documentation
               management.

        6586   PEGASUS - Distributed Multimedia Operating System for the
               1990s This project is aimed at the design of an operating
               system architecture for scalable distributed multimedia
               systems and the development of a validating prototype, the
               design and implementation of a distributed complex-object
               service and a global name service, the development of
               mechanisms for the creation, communication and rendering of
               fully digital multimedia documents in real time and in a
               distributed fashion, and the design and implementation of an
               application for the system: a digital TV director.

        6606   IDOMENEUS - Information and Data on Open Media for Networks
               of Users.  This project, which started January 1993, brings
               together workers in the database, information retrieval,
               networking and hypermedia research communities in the
               development of an "ultimate information machine".  It "will
               coordinate and improve European efforts in the development
               of next-generation information environments capable of
               maintaining and communicating a largely extended class of
               information on an open set of media".  Because of the close
               match between the subject of the IDOMENEUS project and the
               RARE WG-IMM, it is recommended that RARE establish a liaison
               with this project.

    4.5. Other

       Some other research projects of less immediate relevance are listed
       below.  Some of these projects are described further in [1].

          o    Xanadu is a project to develop an "open, social hypermedia"
               distributed database server, incorporating CSCW features.
               It has been in existance for many years and has been funded
               by a number of companies.  The current status of this
               project is not known, and although iminent availability of
               alpha-test versions has been announced more than once, no
               software has been delivered.

          o    CMIFed [15] is an editing and presentation environment for
               portable hypermedia documents being developed at CWI,
               Amsterdam, NL. It is based on the "Amsterdam Model" of

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    RFC 1614        Network Access to Multimedia Information        May 1994

               hypermedia [16], which is an extension of the Dexter
               hypertext reference model incorporating "channels" for media
               delivery and synchronisation constraints.

          o    Deja Vu [17] is a proposed "intelligent" distributed
               hypermedia application framework.  It is intended as a
               vehicle for research in the areas of: hypermedia systems,
               object-oriented programming, distributed logic programming,
               and intelligent information systems.  Proposed techniques
               for use in the Deja Vu framework include "inferential
               links", defined automatically according to predefined rules.
               A scripting language for use both by information providers
               and users is planned.  This project is at a very early
               (proposal) stage, and as yet relatively little software has
               been developed.  Deja Vu is intended principally as a
               research framework rather than as a service tool.

          o    Demon is a project at Bellcore, US,  investigating the
               network requirements of near-term residential multimedia
               services.  The project is designing and implementing an
               experimental application which serves the needs of casual
               multimedia users.

          o    InfoNote is a distributed, multiuser hypermedia system from
               Japan, implemented on a NEC EWS4800 running UNIX and X.
               InfoNote has an editor which can create Japanese texts,
               figures, and raster images.  The same windows are used both
               for editors and browsers. The functionality of the window
               can be changed at any time if data is not write-protected.

          o    MADE - Multimedia Application Demonstration Environment - is
               a project at British Telecom's research laboratory which
               centres on the use of the developing MHEG standard to access
               a multimedia object server.  The server platform is a Sun
               SPARCstation with an object-oriented database package
               (ONTOS).  Audio, video, text and graphical media types are
               covered.  The University of Kent is working on a sub-
               project: "Multi-user Indexing in a Distributed Multimedia
               Database".

          o    Zenith aimed to establish a set of principles to assist
               designers and developers of object management systems
               intended for distributed multimedia design environments.
               The project implemented a prototype generalised multimedia
               object management system.

    Adie                                                           [Page 54]

    RFC 1614        Network Access to Multimedia Information        May 1994

    5. Standards

    5.1. Structuring Standards

       This section describes some of the important standards for providing
       hyperstructure to multimedia data.

       SGML

       SGML (Standard Generalized Markup Language - ISO 8879) is a
       metalanguage for defining markup notations for text.  SGML is used to
       write Document Type Definitions or DTDs, to which individual document
       instances must conform.  It finds application in a wide and
       increasing range of text processing applications.

       The relevance of SGML to distributed hypermedia systems is
       surprisingly high, mainly because of the great expressive power of
       SGML, and its ability to handle non-textual data using "external
       entities" and "notations".

          o    The World-Wide Web is an SGML application with its own DTD.

          o    The important HyTime hypermedia structuring standard (see
               below) is based on SGML.

          o    The forthcoming MHEG hypermedia structuring standard (see
               below) has an SGML encoding.

          o    SGML has been used in research hypermedia systems - for
               example Microcosm.

          o    SGML is used in some commercial hypermedia systems - for
               example DynaText.

          o    SGML is of increasing importance for academic publishing
               houses.

       It was interesting to note that at a recent (CEC-sponsored) workshop
       on Hypertext and Hypermedia standards, most of the speakers were
       conversant with and supportive of the use of SGML for such systems.

       A related standard which may become important for SGML on networks is
       SDIF (SGML Data Interchange Format - ISO 9069).  This standard
       specifies how an SGML document, which may exist in a number of
       separate files of different media types, may be encoded using ASN.1
       into a single bytestream.  The entity structure is preserved, so that
       the bytestream may be decoded by the recipient into the same set of
       files.

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       HyTime

       HyTime (Hypermedia/Time-Based Structuring Language) is a standardised
       infrastructure for the representation of integrated, open hypermedia
       documents.  It was developed principally by ANSI committee X3V1.8M,
       and was subsequently adopted by ISO and published as ISO 10744.

       HyTime is based on SGML.  It is not itself an SGML DTD, but provides
       constructs and guidelines ("architectural forms") for making DTDs for
       describing Hypermedia documents.  For instance, the Standard Music
       Description Language (SMDL: ISO/IEC Committee Draft 10743) defines a
       (meta-)DTD which is an application of HyTime.  In fact, HyTime
       started as an attempt to produce a markup scheme for music publishing
       purposes.

       HyTime specifies how certain concepts common to all hypermedia
       documents can be represented using SGML.  These concepts include:

          o    association of objects within documents with hyperlinks

          o    placement and interrelation of objects in space and time

          o    logical structure of the document

          o    inclusion of non-textual data in the document

       An "object" in HyTime is part of a document, and is unrestricted in
       form - it may be video, audio, text, a program, graphics, etc.  The
       terminology used in HyTime (and in this section) thus differs
       slightly from the terminology used in the rest of this report.  A
       HyTime object corresponds roughly to a node as defined in section
       1.2, and a HyTime document is a hyperdocument in the terminology of
       this report.

       HyTime consists of six modules, which are very briefly and
       selectively described below:

          o    Base module.  This provides facilities required by other
               modules, including a lexical model for describing element
               contents; facilities for identifying policies for coping
               with changes to a document, or traversing a link ("activity
               tracking"); and the ability to define "container entities"
               which can hold multiple data objects.  This last was added
               to the HyTime standard at a late stage, at the instigation
               of Apple Computers Inc, as a "hook" for their Bento
               specification [18].

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          o    Measurement module.  This allows for an object to be located
               in time and/or space (which HyTime treats equivalently), or
               any other domain which can be represented by a finite
               coordinate space, within a bounding box called an "event",
               defined by a set of coordinate points.  Coordinates may be
               expressed in any units (predefined units include
               femtoseconds, fortnights, millenia, angstroms, Northern feet
               and lightyears!).

          o    Location Address module.  In addition to the fundamental
               ability of SGML to identify and refer to elements, this
               module provides a special "named location address"
               architectural form which can be used to refer indirectly to
               data which spans elements, or which is located in external
               entities.  Data may also be addressed indirectly through the
               use of "queries", which return addresses of objects within
               some domain which have properties matching the query.  A
               "HyQ" notation is provided for defining the query.

          o    Hyperlinks module.  Two basic types of hyperlink are
               defined: the contextual link (clink) has two anchors, one of
               which is embedded in a document to explicitly denote the
               anchor location; and the independent link (ilink) which may
               have more than two anchors, and which does not require the
               anchors to be embedded in the document. ilinks thus allow
               hyperlink information to be maintained separately from
               document content.

          o    Scheduling module.  This specifies how events in a source
               finite coordinate space (FCS) are to be mapped onto a target
               FCS.  For instance, events on a time axis could be projected
               onto a spatial axis for graphical display purposes, or a
               "virtual" time axis as used in music could be projected onto
               a physical time axis.

          o    Rendition module.  This allows for individual objects to be
               modified before rendition, in an object-specific way.  One
               example is modification of colours in image so that it can
               be displayed using the currently-selected colour map on a
               graphics terminal, or changing the volume of an audio
               channel according to a user's requirements.

       It is not envisaged that a hypermedia application would need to use
       the entire range of HyTime facilities.  An application designer is
       able to choose appropriate HyTime architectural forms, and to add
       application-specific constraints to them.  The designer may also of
       course use non-HyTime SGML elements and attributes, but these aspects
       of the application can't be understood by a "HyTime engine".  Even in

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    RFC 1614        Network Access to Multimedia Information        May 1994

       the absence of a HyTime engine, the HyTime architectural forms
       provide a useful base of ideas from which a hypermedia system
       designer may wish to work.

       The role of a HyTime engine is not specified in the standard, but
       essentially it is a (sub)program which recognises HyTime constructs
       in document instances and performs application-independent processing
       on them.  For instance, it could interact with multimedia network
       servers to resolve and access hyperlink anchors.  A commercial HyTime
       engine (HyMinder) is under development by TechnoTeacher in the US,
       and the Interactive Multimedia Group at the University of
       Massachusetts - Lowell (contact lrutledg@cs.ulowell.edu) is also
       working on a HyTime engine (HyOctane).

       The Davenport group (a loose consortium of interested companies and
       individuals) is producing a series of standards on hypermedia which
       further constrain the HyTime architectural forms.  One example is the
       SOFABED module [19], which standardises the representation of certain
       kinds of navigational information - tables of contents, indexes and
       glossaries.

       HyTime was envisaged as an interchange format rather than as a format
       for directly-executable hypermedia applications.  It is therefore
       very expressive, but may be difficult to optimise for run-time
       efficiency.

       An attempt has been made [20] to adapt the hyperlink structure in
       WWW's existing HTML DTD to comply with HyTime's clink architectural
       form.  This requires changes to WWW document instances as well as to
       browser software, and in the absence of any immediate benefit it has
       found little favour with the WWW community.  However, it is possible
       that HTML2 will use some aspects of HyTime.

       It is recommended that any further RARE work on networked hypermedia
       should take account of the importance of SGML and HyTime.

       MHEG

       MHEG stands for the Multimedia and Hypermedia information coding
       Experts Group, also known as ISO/IEC JTC1/SC29/WG12 (it used to come
       under SC2).  This group is developing a standard "Coded
       Representation of Multimedia and Hypermedia Information Objects" (ISO
       CD 13522, or CCITT T.171), commonly called MHEG.  The standard is to
       be published in two parts - part 1 being the base notation,
       representing objects using ASN.1, and part 2 being an alternate
       notation which uses SGML.  Part 1 has nearly (June 1993) achieved CD
       status, and is intended to reach full IS in 1994.  Part 2 is intended
       to reach the CD stage in late 1993.

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       MHEG is suited to interactive hypermedia applications such as on-line
       textbooks and encyclopaedia.  It is also suited for many of the
       interactive multimedia applications currently available (in
       platformspecific form) on CD-ROM.  MHEG could for instance be used as
       the data structuring standard for a future home entertainment
       interactive multimedia appliance.  Telecommunications operators are
       interested in MHEG for providing interactive multimedia services
       across ISDN.

       To address such markets, MHEG represents objects in a non-revisable
       form, and is therefore unsuitable as an input format for hypermedia
       authoring applications: its place is perhaps more as an output format
       for such tools.  MHEG is thus not a multimedia document processing
       format - instead it provides rules for the structure of multimedia
       objects which permits the objects to be represented in a convenient
       "final" form with the aim of direct presentation.

       The MHEG draft standard is expressed in object-oriented terms.  The
       main object classes are outlined briefly below.

          o    Content class.  A content object contains the encoded
               (monomedia) information to be presented, along with
               attributes which identify the type of information and the
               encoding method, and mediaspecific attributes such as fonts
               used, sampling rate, image size, etc.

          o    Selection class and Modification class.  The user may
               interact with MHEG objects which inherit interactive
               behaviour from these classes.  (The MHEG object model
               supports multiple inheritance.)

          o    Action class.  Two types of action may be applied to
               objects: projection, which controls how objects are
               rendered; and status actions which affect the state of
               objects.

          o    Link class.  MHEG hyperlinks connect a "start" object with
               one or more "end" objects.  Links consist of a set of
               conditions relating to the state of the start object, and a
               set of actions which are carried out when these conditions
               are satisfied.  Links also define the spatio-temporal
               relationships between objects.

          o    Script class.  Script objects are used to describe more
               complex interobject linkages (e.g., multiple-source links).
               MHEG does not define a scripting language - instead it
               provides a formalism for encapsulating scripts which may be
               executed by an external program (see SMSL below).

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          o    Composite class.  Related objects may be grouped together
               into a single composite object (recursively).  The
               relationships between content objects within a composite
               object are determined by link and script objects which also
               are members of the composite object.

          o    Descriptor class.  Descriptor objects contain general
               information about sets of interchanged objects, so that a
               target system can ensure it has adequate resources to run
               the hypermedia application represented by the object set.

       The relationship between HyTime and MHEG has not yet been fully
       established.  One possible relationship [21] is that an MHEG
       application could be the output of a compilation process which used
       an equivalent HyTime document as input.  This approach would benefit
       both from the expressive power of HyTime and the run-time efficiency
       of MHEG.  However, it has yet to be shown that this is feasible,
       since the capabilities of HyTime and MHEG do not completely overlap.

       There seems to be relatively little interest in or awareness of MHEG
       within the Internet community, which is only just beginning to be
       aware of HyTime.  In view of the draft nature of the MHEG standard,
       this report recommends that RARE should not invest substantial effort
       in MHEG at this time.  However, particularly in view of the interest
       in it shown by PTTs, a watching brief should be kept on MHEG, as it
       may well be relevant in the future.

       ODA

       The Open Document Architecture standard (ODA - ISO 8613 or T.140) is
       a compound document interchange format designed for transferring
       documents between open systems.  It is able to represent documents in
       both a formatted form and a processable (i.e., revisable) form, thus
       allowing both the content and the printed appearance of the document
       to be unambiguously transferred.

       In addition to text data, ODA supports graphics and image data.  A
       revised version to be published in 1993 will support colour.  Future
       developments include support for audio content (underway) and video
       content (planned).  An interface to MHEG is also planned.

       ODA differs from SGML in that the former concerns itself with the
       physical appearance of the document, while SGML deliberately avoids
       doing so.  SGML concerns itself with semantic markup, and can be used
       to describe a wide range of data and document architectures.  ODA has
       a more limited concept of a document.

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       Hypermedia extensions to ODA (HyperODA) are underway.  The extensions
       will support:

          o    References to data held externally to the document (similar
               to SGML's external entities?).

          o    Non-linear structures, using contextual and independent
               hyperlinks based on the HyTime model.

          o    Temporal relationships between document components (e.g.,
               sequential, parallel, cyclic, duration, start delay).

       HyperODA is not being developed in competition to HyTime or MHEG its
       purpose is to add hypermedia features to ODA rather than to be a
       completely general framework for hypermedia applications.

       Bearing in mind that:

          o    the HyperODA extensions are still under development;

          o    in some senses ODA can be seen as a competitor to SGML,
               which has greater presence in the hypermedia world;

          o    there seems to be a lack of enthusiasm for ODA in the
               Internet community (the IETF WG on piloting ODA has
               disbanded);

          o    Adobe's newly-released Acrobat technology (described below)
               will have a significant effect on the marketplace;

       this report recommends that ODA should not form a basis for
       investment in networked hypermedia technology by RARE.

       PREMO

       PREMO (Presentation Environment for Multimedia Objects) is a new work
       item in ISO/IEC JTC1/SC24 (the graphics standards subcommittee).  An
       initial draft [22] exists, and the schedule calls for a CD by June
       1994, a DIS by June 1995, and the final IS by June 1996.

       PREMO addresses the construction of, presentation of, and interaction
       with multimedia objects.  It specifies techniques for creating
       audiovisual interactive single and multiple media applications.  It
       is consistent with the principles of the Computer Graphics Reference
       Model (CGRM, ISO 11072), and is defined in object-oriented terms.

       It is not clear how PREMO relates to HyTime and MHEG.  Although these
       standards are listed in section 2 (References) of the initial draft,

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       they appear not to be mentioned in the text.  The wisdom of
       developing what appears to be yet another structuring standard for
       multimedia data is doubtful.

       The PREMO work is not sufficiently advanced to permit a judgement of
       its usefulness in satisfying the requirements under discussion.

       Acrobat

       Adobe, Inc. has introduced a new format called Acrobat PDF, which it
       is putting forward as a potential de facto standard for portable
       document representation.  Based on the Postscript page description
       language, Acrobat PDF is also designed to represent the printed
       appearance of a document (which may include graphics and images as
       well as text.  Unlike postscript however, Acrobat PDF allows data to
       be extracted from the document.  It is thus a revisable format.  It
       includes support for annotations, hypertext links, bookmarks and
       structured documents in markup languages such as SGML.  PDF files can
       represent both the logical and the formatting structure of the
       document.

       Acrobat PFD thus appears to offer very similar functionality to ODA.
       Adobe's successful Postscript de facto standard profoundly influenced
       information technology - it is possible that if successful, Acrobat
       PDF will be almost as important.  RARE should be aware of this
       technology and its potential impact on multimedia information
       systems.

    5.2. Access Mechanisms

       This section describes some standards which are useful in providing
       network access to multimedia data.  Of course, there are many
       multimedia transport protocols, which this report does not attempt to
       describe (see [1] for further information).  The protocols mentioned
       below are search/retrieve protocols which were not mentioned in [1].

       Multimedia Extensions to SQL

       A new work item in ISO (ISO/IEC JTC1 N2265) to extend the SQL
       standard to include multimedia data is expected to be approved
       shortly.  Initially this work will concentrate on developing a
       framework, and on free text data.  Support for non-text data will be
       added later, using a separate part of the standard for each media
       type.

       The expected timescale for this standardisation work is lengthy (part
       1 - the framework - is targeted for completion in 1996).

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       There are suggestions that this standard could be used as a query
       language in conjunction with the HyQ query component of the HyTime
       standard.

       DFR

       DFR is the Document Filing and Retrieval system, specified in ISO
       10166-1 and ISO 10166-2.  It is intended for office automation
       applications, and falls within the Distributed Office Applications
       (DOA) model of ISO 10031-1.  DFR has design similarities to the ISO
       Directory and to the X.400 Message Store, and it is likewise part of
       OSI.

       DFR defines a Document Store, which provides a service to a DFR User
       over an OSI protocol stack incorporating ROSE (and optionally RTSE).
       A document in the Document Store may have a number of attributes
       associated with it, including pointers to related documents.  There
       is support for multiple versions of the same document, and for
       hierarchical groups of documents.  The access protocol supports
       searching for documents based on their attributes.  DFR itself does
       not restrict the content of documents in any way, but the natural
       partner to DFR is the ODA standard for document content.

       It is not clear that DFR offers significantly more useful
       functionality than is available from other, simpler access protocols
       already in use on the Internet.

    5.3. Other Standards

       This section briefly describes other standards in this area and
       discusses their relevance.

       MIME

       MIME (Multipurpose Internet Mail Extensions) is a mechanism for
       transferring multimedia information in an RFC822 mail message.  STD
       11, RFC 822 defines a message representation protocol which specifies
       considerable detail about message headers, but which leaves the
       message content as flat ASCII text.  RFC 1341 redefines the format of
       message bodies to allow multi-part textual and non-textual message
       bodies to be represented and exchanged without loss of information.
       Because RFC 822 said very little about message content, RFC 1341 is
       largely orthogonal to (rather than a revision of) RFC 822.

       MIME provides facilities to include multiple objects in a single
       message, to represent text in character sets other than US-ASCII, to
       represent formatted multi-font text messages, to represent non
       textual material such as images and audio fragments, and generally to

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       facilitate later extensions defining new types of Internet mail for
       use by co-operating mail agents.  It does not define any structure to
       allow relationships between body parts within a message to be
       expressed.

       For the purposes of the requirements considered by this report, the
       relevance of MIME is that it separates media type from media
       encoding, and that it defines a procedure for registering values of
       these attributes.

       The MIME construct of chief interest is the "Content-Type" field.
       This contains a MIME "type" and "subtype", and any "parameters" which
       further qualify the subtype.  The register of MIME content-types is
       maintained by the Internet Assigned Numbers Authority (IANA). Content
       types defined in the MIME standard itself include:

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        Type            Subtype       Parameters    Meaning

        text            plain         charset       Plain text

                        richtext      charset       Text with SGML-like
                                                    markup for
                                                    representing
                                                    formatting.

        image           jpeg                        JPEG File Interchange
                                                    Format

                        gif                         Graphics Interchange
                                                    Format

        audio           basic                       8-bit -law 8kHz PCM
                                                    encoding

        video           mpeg

        application     ODA           profile       Open Document
        (used                         (Document     Architecture
        for                           Application   document.
        application                   Profile)
        -specific
        data)

                        octet-        name (e.g.,   General binary data
                        stream        filename);    such as an arbitrary
                                      type (for     binary file.
                                      human
                                      recipient),
                                      etc.

                        postscript                  Document in
                                                    postscript.

       Private experimental values of types and subtypes starting with X may
       be used between consenting adults without registration with IANA.

       MIME also defines a "Content-Transfer-Encoding" field, which is used
       to specify an invertible mapping between the "native" encoding of a
       media type and a representation that may be readily exchanged using
       7bit mail transfer protocols.

       WWW's HTTP2 protocol makes use of MIME media type and encoding
       attributes, and also uses MIME's message format for retrieving data

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       from the server.  It is the first MIME application to utilise the
       8bit Content-Transfer-Encoding, which essentially means no encoding.

       SMSL

       SMSL is the Standard Multimedia Scripting Language.  It is a proposed
       new work item for ISO/IEC JTC1/SC18/WG8 (HyTime) and JTC1/SC29/WG12
       (MHEG).  The functional requirements are expected to be completed in
       1994, and the coding scheme completed in 1995.

       SMSL is designed as an open language with a similar purpose to
       existing vendor-specific scripting languages such as Macromind's
       "Lingo", Kaleida's "Script/X", and Gain's "GEL".  The intention is to
       offer an intermediate open multimedia scripting language which could
       be used both for interchange purposes, and for controlling the
       presentation of HyTime or MHEG multimedia structures.  Several
       different approaches to defining SMSL have been suggested, including
       using the ANDF (Architecture-Neutral Distribution Format) approach,
       and basing SMSL on SGML or on the Scheme language.

       The SMSL work is not sufficiently advanced to permit a judgement of
       its usefulness in satisfying the requirements under discussion.
       However, it is interesting to note that despite the descriptive power
       of HyTime and MHEG, there is still perceived to be a role for
       procedural scripting.

       AVIs

       The CCITT is defining a set of Audio Visual Interactive Services
       (AVIs), intended for offering to domestic and business consumers over
       a national network (e.g., by PTTs).  These services will be specified
       as T.17x recommendations, and will include MHEG.  These services
       would also make use of the SMSL work.

       Insufficient information is available about this area to allow its
       relevance to be judged.

    5.4. Trade Associations

       This section mentions some trade associations which are involved in
       standards making in the multimedia area.

       Interactive Multimedia Association

       The Interactive Multimedia Association (IMA) is an international
       trade association with over 250 members, representing a wide spectrum
       of multimedia industry players.  Members include Apple, Microsoft,
       MIT CECI (the developers of AthenaMuse 2), 3DO, and many other

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       important market actors.

       In 1989, the IMA initiated a "Compatibility Project", tasked with
       developing technical solutions to the cross-platform compatibility
       problem.  The Project has published two important documents:

          o    "Recommended Practices for Multimedia Portability" [23]
               outlines a specification for a common interface to be used
               by interactive video delivery systems.  It has been adopted
               by the US Military as part of Military Standard 1379.

          o    "Recommended Practices for Enhancing Digital Audio
               Compatibility in Multimedia Systems" [24] defines four
               standard digital audio data types and four sampling rates
               (from low-end -law 8kHz mono encoding, up through ADPCM
               modes to CD-quality 44kHz 16-bit stereo).

       Work is continuing to produce further recommendations on other
       issues.

       The Compatibility Project has now initiated a procurement process by
       publishing three Request for Technology (RFT) documents, defining the
       requirements of a platform-independent interactive multimedia system,
       including networking requirements.  The RFTs cover "Multimedia System
       Services", a "Scripting Language for Interactive Multimedia Titles",
       and "Multimedia Data Exchange".  An "Architecture Reference Model"
       for cross-platform desktop and distributed multimedia systems
       provides the framework for these RFTs, which are pragmatic documents
       outlining the technical requirements for time-based media handling in
       detail.  Note that relatively little is said about non-time-based
       data.

       A first reading of the Multimedia Data Exchange RFT reveals that the
       Apple Bento standard [18] and the Microsoft/IBM RIFF format [25] both
       influenced the development of this document.  The selected system may
       well be based on one or both of these technologies.

       A joint response to the Multimedia System Services RFT has been
       received from HP, IBM and Sun.  Two responses to the Scripting
       Languages RFT have been received - from Kaleida (Script-X) and Gain
       Technology (GEL).  Two partial responses to the Multimedia Data
       Exchange RFT have been received from Apple (Bento) and Avid (Open
       Media Framework).

       Responses to the RFTs are currently being analysed by the IMA, and
       the result will be announced in November 1993.  The specifications
       which will eventually result from this process will be important for
       future commercial multimedia products.  It is important that the

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       community keep a watching brief on the IMA Compatibility Project and
       its possible implications for distributed multimedia applications on
       the Internet.

       Multimedia Communications Forum

       The Multi-Media [sic] Communications Forum (MMCF) is a recently
       formed (June 1993) trade consortium whose initial members include
       IBM, National Semiconductor, Apple, Siemens and AT&T.  Intended to
       complement the work of the IMA, the MMCF plans to develop guidelines
       and recommendations for the industry to help ensure "end-to-end
       network interconnectivity of multimedia applications, workstations
       and devices".  They also plan to provide input to standards bodies.

       It is still too early to say whether this forum will succeed.  If the
       IMA Compatibility Project specifications, when they are published,
       leave networking issues open, then MMCF could have an important role
       to play.  It is recommended that RARE consider becoming an Observing

       Member ($350 US pa), entitling it to attend general and annual MMCF
       meetings (but not committee meetings), and to receive minutes and
       other general papers (but not working documents); with the prospect
       of becoming an Auditing Member ($1200 US pa) later if relevant.

       Multimedia Communications Community of Interest

       This is a very new organisation formed at a meeting in France in June
       1993.  Its charter is to promote the use of applications which let
       people in different locations view documents, images, graphics and
       full-motion video on a PC screen.  The remit includes CSCW aspects.
       Members of the organisation include IBM, Intel, Northern Telecom,
       Telstra (Australia), BT, France Telecom and DB Telekom.  The
       companies plan field trials of multimedia services in 1Q94.

    6. Future Directions

    6.1. General Comments on the State-of-the-Art

       Distributed hypermedia systems are now emerging from the research
       phase into the experimental deployment stage.  Every project team
       (and standards committee), almost without exception, hopes for their
       system to become the de facto standard for hypermedia.

       As we've seen, Gopher and WWW already offer multimedia capability,
       but they are still largely oriented to the use of external viewers
       for non-text nodes.  This "unintegrated" approach is in contrast to
       typical stand-alone multimedia applications, where the presentation
       of related information in different media is tightly integrated.  The

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       in-line image feature of XMosaic and the new version of HTML
       currently under development may represent the start of a move towards
       greater integration of different media in such distributed hypermedia
       systems.

       Three important factors in the design of distributed hypermedia
       systems appear to emerge from the preceding chapters of this report.
       They can each be formulated in terms of distinctions between two
       aspects of the system.

          o    A common and apparently fruitful approach to hypermedia
               systems is to distinguish the content from the
               hyperstructure.  Standards work clearly distinguishes
               between these concepts, with standards such as MPEG, JPEG,
               G.72x, etc, for content; and HyTime or MHEG for structure.
               Currently-deployed systems also make this distinction, most
               obviously in Gopher, where the structure/content split maps
               onto the server filesystem's directory/file split.  In a
               similar way, the ability to maintain hyperlink information
               separately from data is perceived in hypermedia research
               circles as a "good thing".  Research systems such as
               Microcosm and Hyper-G do this, and HyTime with its ilink
               element also supports it.  WWW does not support this, but
               requires link anchors to be edited into source data.  There
               are problems with this approach, however - see the section
               on Microcosm for details.

          o    A useful approach to content is to distinguish the media
               type from the media encoding.  The MIME standard (used by
               HTTP2) illustrates how this can be done, and Gopher+ employs
               a similar system.

          o    The distinction between data and protocol is also important
               for some systems.  WWW for instance has clearly separate
               protocol (HTTP) and data (HTML) specifications.  However,
               Gopher+ is specified without making this distinction.  (The
               original Gopher system is very simple and arguably has no
               need for such separation.)

       The most significant mismatches between the capabilities of
       currentlydeployed systems and user requirements are in the areas of
       presentation and quality of service.  Adding flexibility in
       presentation capabilities to WWW or Gopher should be possible without
       any major change to the protocols (although it may require changes to
       data formats).  Such capabilities could result from the progress
       towards greater integration of media types presaged above.  However,
       improving QOS is significantly more difficult, as it may require
       changes at a more fundamental level.  The following section outlines

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       some possible solutions to this problem.

    6.2. Quality of Service

       Meeting the responsiveness requirement is certainly the key factor
       for the acceptance of networked multimedia information systems in the
       user community.  To reiterate the requirement given in a previous
       section:

          o    For simple actions such as "next page", tolerable delays are
               of the order of 0.2s.

          o    For more complex actions such as "search for documents
               containing this word", then a tolerable delay is of the
               order of 2s.

          o    Users tend to give up waiting for a response after about
               20s.

       There are several methods which may alleviate the problem of poor
       responsiveness (or cause the user to revise his or her expectations
       of responsiveness!), some of which are described below.

          1.   Give clues that fetching a particular item might be time-
               consuming - simply quoting the size (and/or location) may be
               sufficient. WAIS and some Gopher clients already quote the
               size.

          2.   Display a "progress" indicator while fetching data.

          3.   Allow the user to interact with other, previously fetched
               information while waiting for data to be retrieved.  The
               inability to do this is an annoying limitation of XMosaic.
               It can be difficult to implement, except on a multi-threaded
               operating system such as OS/2 or Windows NT.

          4.   Allow several fetches to be performed in parallel.  Again,
               multithreading support makes this easier.  This technique is
               less likely to be useful if all the nodes being requested
               come from the same server.
          5.   Pre-fetch information which the client software believes the
               user will wish to see next.  This requires some "hints" in
               the data about which nodes might be good candidates for pre-
               fetching.

          6.   Cache information locally.  The use of Universal Resource
               Numbers (see the section on WWW) is relevant for managing
               this.

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          7.   Where multiple copies of the same information are held in
               different network locations, fetch the "nearest" copy.  This
               is sometimes known as "anycasting", and is a more general
               case of local caching.  The proposed URN-to-URL resolution
               service [26] could be used to support this.

          8.   When retrieving a document, the client should be able to
               display the first part of the document to the user.  The
               user can then start to read the document while the system is
               still downloading it.  Alternatively, the user may decide
               that the document is not relevant and abort the retrieval.

          9.   Offer multiple views of image or video data at different
               resolutions and therefore sizes.  This enables the user to
               select a balance between speed of retrieval and data
               quality.  Gopher+ and HTML2 both support this.

          10.  Future high-speed networks and protocols (ATM, RTP) will
               allow real-time display of isochronous data.  Information
               systems should be able to take advantage of this.

       A useful description of the problem is given in [27].  This paper
       rightly contends that the view, held by many hypermedia researchers
       and implementors, that the network is simply a transparent data
       highway which needs no special consideration in application design,
       is wrong.  It is argued that:

                   "the very same structural characteristics that may make
                   a multimedia document appealing to the end user are the
                   characteristics that are extremely helpful during
                   dynamic network performance optimisation".

       This is a particularly relevant statement considered in the light of
       suggestion 5 above.

    6.3. Recommended Further Work

       To meet the needs of applications such as those described in section
       2.1, the community must seek where possible to adapt and enhance
       existing tools, not to build new ones.  There is now an opportunity
       for RARE to stimulate and encourage this process of adaptation and
       enhancement, and the following subsections outline a strategy for
       this.

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       Selecting a System

       In order to have the greatest effect, RARE should concentrate its
       efforts on only one of the existing tools.  Candidate technologies
       are those already outlined: Gopher, WWW, WAIS, Hyper-G, Microcosm and
       AthenaMuse 2.

       It is recommended that RARE should select the World-Wide Web to
       concentrate its efforts on.  The reasons for this decision are as
       follows.

          o    Flexibility.  The rich yet straightforward design of WWW,
               with its clearly separable components (HTML, URL and HTTP),
               means that it is a very flexible basis on which to develop
               distributed multimedia applications.

          o    Existing efforts.  The WWW implementor community is already
               discussing and designing extensions to HTML (HTML2),
               intended (among other things) to support multimedia.  There
               is clearly much interest in this area, and RARE efforts
               could complement existing work.

          o    Hyperlinks.  A clear requirement of many applications is the
               availability of hyperlinking, which WWW supports well.

          o    Integrated solution.  Because WAIS, Gopher and Hyper-G (as
               well as anonymous FTP servers) may all be accessed from Web
               clients, WWW serves as an important integrating tool for
               information services. It is important that distributed
               multimedia applications, which require extensive support in
               the client software, should be based on a technology "close
               to" such integrated clients.

          o    Penetration and growth.  Although Gopher far surpasses WWW
               in the number of servers available, the rate of growth in
               WWW usage is greater than that of Gopher.  There is an
               increasing realisation in the community that Gopher is over-
               simplistic for many purposes, and a corresponding increase
               in interest in WWW.

          o    Attention to QOS issues.  There is already an awareness in
               the WWW community of the need for achieving an appropriate
               QOS, and a mechanism has already been proposed in HTTP2 to
               alleviate the problem.

          o    Standardisation.  The WWW team is taking standardisation of
               the existing WWW system components seriously.  The URL
               format has already been published as an Internet draft (and

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               has been adopted as an important component of the proposed
               Internet integrated information infrastructure), and the
               current version of HTML is about to follow suit.  The use of
               SGML as the basis of HTML complies with the perceived
               importance of SGML for hypermedia in general (and also fits
               in with RARE's approach of adopting appropriate open
               standards).

          o    Software status.  CERN has recently placed the WWW code
               developed by it into the public domain.  This is unlike all
               the other candidate technologies, which all have
               restrictions on who can do what with the code.  In the case
               of Gopher, these restrictions are already causing some
               commercial users to look at other options.

       WWW has two significant disadvantages, both of which are being
       alleviated:

          o    Restricted choice of client software.  At present, Apple
               Macintosh and PC/MS Windows clients are available in beta
               form only.  By contrast, there are more than one well-tested
               Gopher clients available for these platforms.

               However, other WWW clients for the Mac and MS Windows are in
               the pipeline.

          o    There is a perception in the community that making
               information available over HTTP is difficult, and that it
               must be put into HTML.

               However, it is possible to put plain-text, non-HTML
               documents onto the Web.  Such documents of course cannot
               contain links.

               Furthermore, WYSIWYG HTML text editors are available, to
               ease the pain of writing HTML.

       The main disadvantages of the other systems are:

          o    Gopher is designed for simplicity, and therefore lacks the
               flexibility of WWW.  In particular its structure is too
               inflexibly hierarchical and it does not have hyperlinks.
               Its main advantage is its very heavy penetration.  However,
               because of the WWW approach to accessing data using other
               protocols, all of gopherspace is part of the Web.  Any Web
               client should be able to be a gopher client too.

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    RFC 1614        Network Access to Multimedia Information        May 1994

               It is neither envisaged that Gopher will go away, nor that
               it won't be used for multimedia data.  However, Gopher is
               unlikely to be used for more sophisticated multimedia
               applications such as academic publishing, interactive
               multimedia databases and CAL, because of the above-mentioned
               limitations.

          o    WAIS is a specialised tool, and will certainly form part of
               the overall solution, particularly for database-type
               applications.  It is not a general solution for distributed
               hypermedia applications.

          o    AthenaMuse 2 is commercially-oriented: it is clear that
               academic and research users will have to pay to use the
               software.  Its level of use is thus very unlikely to be as
               great as publiclyavailable systems such as WWW.  Moreover,
               it does not support all the required platforms.

          o    Microcosm network support is still in early stages, limited
               at present to the PC/Windows platform.  If it can be shown
               to perform adequately over a network, if it is capable of
               scaling to global levels, and if the advantages of
               maintaining link information separately from documents are
               found clearly to outweigh the consequent difficulties, it
               may become important in the future. Microcosm's authors need
               to ensure that the commercialisation of Microcosm does not
               hinder its adoption by the academic community.

          o    Hyper-G is more difficult to dismiss.  It is still in a
               relatively early stage of development, but appears to have
               many of the necessary features.  Its main disadvantages are:
               (a) the lack of penetration outside the University of Graz -
               the author is aware of only one other site using it; and (b)
               it is currently limited to UNIX only.  The author believes
               that, given WWW's head start in terms of deployment, and the
               current progress in adding multimedia facilities to it, WWW
               stands a much better chance than Hyper-G of being accepted
               as the de facto standard for distributed multimedia
               applications on the Internet.

       Directions for RARE

       Earlier in this report, it was noted that the most important areas
       where effort was needed were (a) provision of facilities for the
       integrated presentation of multimedia data (including synchronisation
       issues); and (b) ensuring adequate responsiveness.

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    RFC 1614        Network Access to Multimedia Information        May 1994

       Bearing this in mind, it is recommended that RARE should invite
       proposals and (subject to funding being available) subsequently
       commission work to:

          1.   Develop conversion tools from commercial authoring packages
               to WWW, and establish authoring guidelines for authors who
               wish to use the conversion tools.  This is a significant and
               high-profile development aimed at enabling sophisticated
               multimedia applications to run over the network.  (Authoring
               guidelines will be necessary to enable authors to fit in
               with the Web's way of doing things, and to document features
               of the authoring package which should be avoided because of
               conversion difficulties.)

          2.   Implement and evaluate the most promising ways of overcoming
               the QOS problem.  This is an essential task without which
               interactive distributed multimedia applications cannot
               become a reality.  Some possibilities have already been
               outlined in the preceding chapter.

          3.   Implement a specific user project using these tools, in
               order to validate that the facilities being developed are
               truly relevant to actual user requirements.  It may be that
               partner funding from the selected user project would be
               appropriate.

          4.   Use the experience gained from 1, 2 and 3 to inform and
               influence the further development of HTML2 and HTTP2 to
               ensure that they provide the required facilities.

          5.   Contribute to the development of the WWW clients
               (particularly the Apple Macintosh and PC/MS Windows clients)
               in terms of their multimedia data handling facilities.

       Although it is strictly speaking outside the remit of this report
       (since it is not specifically concerned with multimedia data), it is
       noted that the rapid growth of WWW may in the future lead to problems
       through the implementation of multiple, uncoordinated and mutually
       incompatible add-on features.  To guard against this trend, it may be
       appropriate for RARE, in coordination with CERN and other interested
       parties such as NCSA, to:

          6.   Encourage the formation of a consortium to coordinate WWW
               technical development (protocol enhancements, etc).

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    RFC 1614        Network Access to Multimedia Information        May 1994

    7. References

          [1]         "A Survey of Distributed Multimedia Research,
                      Standards and Products", ed. C. Adie, January 1993
                      (RARE Technical Report 5).
                      URL=ftp://ftp.ed.ac.uk/pub/mmsurvey/

          [2]         "The Dexter Hypertext Reference Model", F. Halasz and
                      M. Schwartz, NIST Hypertext Standardisation Workshop,
                      January 1990.

          [3]         "Response Time and Display Rate in Human Performance
                      with Computers", B. Shneiderman, Comp. Surveys 16,
                      1984.

          [4]         "Gopher+: Proposed Enhancements to the Internet
                      Gopher Protocol", B. Alberti, F. Anklesaria, P. Linder,
                      M. McCahill, D. Torrey, Summer 1992.
                      URL=gopher://boombox.micro.umn.edu:70/11/gopher/gop
                      her_protocol/Gopher%2b

          [5]         "WAIS Interface Protocol", F. Davies, B. Kahle, H.
                      Morris, J. Salem, T. Shen, R. Wang, J. Sui and M.
                      Grinbaum, April 1990.
                      URL=ftp://quake.think.com/wais/doc/protspec.txt

          [6]         "Uniform Resource Locators", T. Berners-Lee, March
                      1993.  URL=ftp://info.cern.ch/pub/ietf/url4.ps

          [7]         "The HTTP Protocol as Implemented in W3", T. Berners-
                      Lee, January 1992.
                      URL=ftp://info.cern.ch/pub/www/doc/http.txt

          [8]         "Protocol for the Retrieval and Manipulation of
                      Textual and Hypermedia Information", T. Berners-Lee,
                      1993.  URL=ftp://info.cern.ch/pub/www/doc/httpspec.ps

          [9]         "Hypertext Markup Language (HTML)", T Berners-Lee,
                      March 1993. URL=ftp://info.cern.ch/pub/www/doc/html-
                      spec.ps

          [10]        "Hyper-G: A Universal Hypermedia System", F. Kappe and
                      N. Sherbakov, March 1992. URL=ftp://iicm.tu-
                      graz.ac.at/pub/HyperG/doc/report333.txt.Z

    Adie                                                           [Page 76]

    RFC 1614        Network Access to Multimedia Information        May 1994

          [11]        "Towards an Integrated Information Environment with
                      Open Hypermedia Systems", H. Davis, W. Hall, I. Heath,
                      G. Hill, Proceedings of the ACM Conference on
                      Hypertext, Milan 1992, p181-190.

          [12]        "The AthenaMuse 2 Functional Specification", L.
                      Bolduc, J. Culbert T. Harada, J. Harward, E.
                      Schlusselberg, May 1992.
                      URL=ftp://ceci.mit.edu/pub/AM2/funcspec.txt.Z

          [13]        "Research and Technology Development in Advanced
                      Communications Technologies in Europe: RACE '92",
                      CEC, March 1992.  Available from:
                      raco@postman.dg13.cec.be

          [14]        "Esprit Programme Synopses", CEC, October 1992.  In
                      seven volumes.  Available from
                      esprit_order_mailbox@eurokom.ie

          [15]        "CMIFed: A Presentation Environment for Portable
                      Hypermedia Documents", G. van Rossum, J. Jansen, K. S.
                      Mullender, D. C. A. Bulterman, Amsterdam 1993 (also
                      presented at ACM Multimedia 93 conference).
                      URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9305.ps.Z

          [16]        "The Amsterdam Hypermedia Model: extending hypertext
                      to support real multimedia", L. Hardman, D. C. A.
                      Bulterman, G. van Rossum, Amsterdam 1993
                      URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9306.ps.Z

          [17]        "Deja-Vu Distributed Hypermedia Application
                      Framework", A. Eliens.
                      URL=ftp://ftp.cs.vu.nl/eliens/Deja-Vu-proposal.ps

          [18]        "Bento Specification", J. Harris and I. Ruben, Apple
                      Computer Inc, August 1992.
                      URL=ftp://ftp.apple.com/apple/standards/Bento_1.0d4.1

          [19]        "Davenport Advisory Standard for Hypermedia (DASH),
                      Module I: Standard Open Formal Architecture for
                      Browsable Hypermedia Documents (SOFABED)", ed S. R.
                      Newcomb and V. T. Newcomb.
                      URL=ftp://sgml1.ex.ac.uk/davenport/sofabed.0.9.6.ps.Z

          [20]        Article in comp.text.sgml newsgroup, 24 May 1993, by
                      Eliot Kimber (drmacro@vnet.ibm.com).
                      URL=ftp://ftp.ifi.uio.no/SGML/comp.text.sgml/by.msg
                      id/19930524.152345.29@almaden.ibm.com

    Adie                                                           [Page 77]

    RFC 1614        Network Access to Multimedia Information        May 1994

          [21]        "Emerging Hypermedia Standards" B. Markey, Multimedia
                      for Now and the Future (Usenix Conference
                      Proceedings), June 1991.

          [22]        "Initial Draft PREMO (Presentation Environment for
                      Multimedia Objects", ISO/IEC JTC1/SC24 N847, November
                      1992.

          [23]        "Recommended Practices for Multimedia Portability",
                      Release 1.1 October 1990, Interactive Multimedia
                      Association, 3 Church Circle, Suite 800, Annapolis,
                      MD 21401-1993, USA.

          [24]        "Recommended Practices for Enhancing Digital Audio
                      Compatability in Multimedia Systems", Release 3.00
                      1992, Interactive Multimedia Association, 3 Church
                      Circle, Suite 800, Annapolis, MD 21401-1993, USA.

          [25]        "RIFF Tagged File Format", Microsoft Inc, 1992.

          [26]        "A Vision of an Integrated Internet Information
                      Service", C. Weider and P. Deutsch, March 1993,
                      Work in Progress.

          [27]        "Delivering Interactive Multimedia Documents over
                      Networks", S. Loeb, IEEE Communications Magazine, May
                      1992.

          [28]        "A Status Report on Networked Information Retrieval:
                      Tools and Groups", ed. J. Foster, G. Brett and P.
                      Deutsch, March 1993.
                      URL=ftp://mailbase.ac.uk/pub/nir/nir.status.report

    Adie                                                           [Page 78]

    RFC 1614        Network Access to Multimedia Information        May 1994

    8. Security Considerations

       Security issues are not discussed in this memo.

    9. Author's Address

       Chris Adie
       Edinburgh University Computing Service
       University Library
       George Square
       Edinburgh EH8 9LJ
       United Kingdom

       Phone: +44 31 650 3363
       Fax:   +44 31 662 4809
       EMail: C.J.Adie@edinburgh.ac.uk

    Adie                                                           [Page 79]