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RFC 1614 - Network Access to Multimedia Information


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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

      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.

   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.

   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.

      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.

      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".

   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

   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.

   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.

      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.

   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".

    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.

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.

   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.

      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.

      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.

   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

   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.

      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

   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.

   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

           (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.)

   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).

   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

        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.

   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.

        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:

    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>

   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.

   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

   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.

   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

   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.

   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

        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.

   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.

   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).

   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:

    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:

      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.

   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.

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).

      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.

   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.

   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

    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.

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

   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.

      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.

      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

           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.

    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.

    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

           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.

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.

   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].

      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

   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.

   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).

      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.

   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,

   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).

   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

   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:

    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

   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

   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

   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

   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

   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.

      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.

   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

           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.

           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.

   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).

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

      [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

      [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

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

 

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