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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

Adie [Page 1] RFC 1614 Network Access to Multimedia Information May 1994

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

Acknowledgements

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

Disclaimer

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

Adie [Page 2] RFC 1614 Network Access to Multimedia Information May 1994

 The opinions expressed in this report are personal opinions of the
 author.  They do not necessarily represent the policy either of RARE
 or of ECUS.
 Mention of a product in this report does not constitute endorsement
 either by EUCS or by RARE.

Availability

 This document is available in various forms (PostScript, text,
 Microsoft Word for Windows 2) by anonymous FTP through the following
 URL:
  ftp://ftp.edinburgh.ac.uk/pub/mmaccess/
  ftp://ftp.rare.nl/rare/pub/rtr/rtr8-rfc.../
  Paper copies are available from the RARE Secretariat.

0. Extended Summary

 Introduction
 This report is concerned with issues in the intersection of
 networked information retrieval, database and multimedia
 technologies.  It aims to establish research and academic user
 requirements for network access to multimedia data, to look at
 existing systems which offer partial solutions, and to identify
 what needs to be done to satisfy the most pressing requirements.
 User Requirements
 There are a number of reasons why multimedia data may need to be
 accessed remotely (as opposed to physically distributing the data,
 e.g., on CD-ROM).  These reasons centre on the cost of physical
 distribution, versus the timeliness of network distribution.  Of
 course, there is a cost associated with network distribution, but
 this tends to be hidden from the end user.
 User requirements have been determined by studying existing and
 proposed projects involving networked multimedia data.  It has
 proved convenient to divide the applications into four classes
 according to their requirements: multimedia database applications,
 academic (particularly scientific) publishing applications, cal
 (computeraided learning), and general multimedia information
 services.

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 Database applications typically involve large collections of
 monomedia (non-text) data with associated textual and numeric
 fields. They require a range of search and retrieval techniques.
 Publishing applications require a range of media types,
 hyperlinking, and the capability to access the same data using
 different access paradigms (search, browse, hierarchical, links).
 Authentication and charging facilities are required.
 Cal applications require sophisticated presentation and
 synchronisation capabilities, of the type found in existing
 multimedia authoring tools.  Authentication and monitoring
 facilities are required.
 General multimedia information services include on-line
 documentation, campus-wide information systems, and other systems
 which don't conveniently fall into the preceding categories.
 Hyperlinking is perhaps the most common requirement in this area.
 The analysis of these application areas allows a number of
 important user requirements to be identified:
    o    Support for the Apple Macintosh, UNIX and PC/MS Windows
         environments.
    o    Support for a wide range of media types - text, image,
         graphics and application-specific media being most
         important, followed by video and sound.
    o    Support for hyperlinking, and for multiple access structures
         to be built on the same underlying data.
    o    Support for sophisticated synchronisation and presentation
         facilities.
    o    Support for a range of database searching techniques.
    o    Support for user annotation of information, and for user-
         controlled display of sequenced media.
    o    Adequate responsiveness - the maximum time taken to retrieve
         a node should not exceed 20s.
    o    Support for user authentication, a charging mechanism, and
         monitoring facilities.
    o    The ability to execute scripts.

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    o    Support for mail-based access to multimedia documents, and
         (where appropriate) for printing multimedia documents.
    o    Powerful, easy-to-use authoring tools.
 Existing Systems
 The main information retrieval systems in use on the Internet are
 Gopher, Wais, and the World-Wide Web.  All work on a client-server
 paradigm, and all provide some degree of support for multimedia data.
 Gopher presents the user with a hierarchical arrangement of nodes
 which are either directories (menus), leaf nodes (documents
 containing text or other media types), or search nodes (allowing some
 set of documents to be searched using keywords, possibly using WAIS).
 A range of media types is supported.  Extensions currently being
 developed for Gopher (Gopher+) provide better support for multimedia
 data.  Gopher has a very high penetration (there are over 1000 Gopher
 servers on the Internet), but it does not provide hyperlinks and is
 inflexibly hierarchical.
 Wais (Wide Area Information Server) allows users to search for
 documents in remote databases.  Full-text indexing of the databases
 allows all documents containing particular (combinations of) words to
 be identified and retrieved.  Non-text data (principally image data)
 can be handled, but indexing such documents is only performed on the
 document file name, severely limiting its usefulness.  However, WAIS
 is ideally suited to text search applications.
 World-Wide Web (WWW) is a large-scale distributed hypermedia system.
 The Web consists of nodes (also called documents) and links.  Links
 are connections between documents: to follow a link, the user clicks
 on a highlighted word in the source document, which causes the
 linkedto document to be retrieved and displayed.  A document can be
 one of a variety of media types, or it can be a search node in a
 similar sense to Gopher.  The WWW addressing method means that WAIS
 and Gopher servers may also be accessed from (indeed, form part of)
 the Web.  WWW has a smaller penetration than Gopher, but is growing
 faster.  The Web technology is currently being revised to take better
 account of the needs of multimedia information.
 These systems all go some way to meet the user requirements.
    o    Support for multiple platforms and for a wide range of media
         types (through "viewer" software external to the client
         program) is good.
    o    Only WWW has hyperlinks.

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    o    There is little or no support for sophisticated presentation
         and synchronisation requirements.
    o    Support for database querying tends to be limited to
         "keyword" searches, but current developments in Gopher and
         WWW should make more sophisticated queries possible.
    o    Some clients support user annotation of documents.
    o    Response times for all three systems vary substantially
         depending on the network distance between client and server,
         and there is no support for isochronous data transfer.
    o    There is little in the way of authentication, charging and
         monitoring facilities, although these are planned for WWW.
    o    Scripting is not supported because of security issues
    o    WWW supports a mail responder.
    o    The only system sufficiently complex to warrant an authoring
         tool is WWW, which has editors to support its hypertext
         markup language.
 Research
 There are a number of research projects which are of significant
 interest.
 Hyper-G is an ambitious distributed hypermedia research project at
 the University of Graz.  It combines concepts of hypermedia,
 information retrieval systems and documentation systems with aspects
 of communication and collaboration, and computer-supported teaching
 and learning.  Automatic generation of hyperlinks is supported, and
 there is a concept of generic structures which can exist in parallel
 with the hyperlink structure.  Hyper-G is based on UNIX, and is in
 use as a CWIS at Graz.  Gateways between Hyper-G and WWW exist.
 Microcosm is a PC-based hypermedia system developed at the University
 of Southampton.  It can be viewed as an integrating hypermedia
 framework - a layer on top of a range of existing applications which
 enables relationships between different documents to be established.
 Hyperlinks are maintained separately from the data.  Networking
 support for Microcosm is currently under development, as are versions
 of Microcosm for the Apple Macintosh and for UNIX.  Microcosm is
 currently being "commercialised".

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 AthenaMuse 2 is an ambitious distributed hypermedia authoring and
 presentation system under development by a university/industry
 consortium based at MIT.  It will have good facilities for
 presentation and synchronisation of multimedia data, strong authoring
 support, and will include support for networking isochronous data. It
 will be a commercial product.  Initial versions will support UNIX and
 X windows, with a PC/MS Windows version following.  Apple Macintosh
 support has lower priority.
 The "Xanadu" project is designing and building an "open, social
 hypermedia" distributed environment, but shows no sign of delivering
 anything after several years of work.
 The European Commission sponsors a number of peripherally relevant
 projects through its Esprit and RACE research programmes.  These
 programmes tend to be oriented towards commercial markets, and are
 thus not directly relevant.  An exception is the Esprit IDOMENEUS
 project, which brings together workers in the database, information
 retrieval and multimedia fields.  It is recommended that RARE
 establish a liaison with this project.
 There are a variety of other academic and commercial research
 projects which are also of interest.  None of them are as directly
 relevant as those outlined above.
 Standards
 There are a number of existing and emerging standards for structuring
 hypermedia applications.  Of these, the most important are SGML,
 HyTime, MHEG, ODA, PREMO and Acrobat.  All bar the last are de jure
 standards, while Acrobat is a commercial product which is being
 proposed as a de facto standard.
 SGML (Standard Generalized Markup Language) is a markup language for
 delimiting the logical and semantic content of text documents.
 Because of its flexibility, it has become an important tool in
 hypermedia systems.  HyTime is an ISO standardised infrastructure for
 representing integrated, open hypermedia documents, and is based on
 SGML.  HyTime has great expressive power, but is not optimised for
 run-time efficiency.  It is recommended that future RARE work on
 networked hypermedia should take account of the importance of SGML
 and HyTime.
 MHEG (Multimedia and Hypermedia information coding Experts Group) is
 a draft ISO standard for representing hypermedia applications in a
 platform-independent form.  It uses an object-oriented approach, and
 is optimised for run-time efficiency.  Full IS status for MHEG is
 expected in 1994.  It is recommended that RARE keep a watching brief

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 on MHEG.
 The ODA (Open Document Architecture) standard is being enhanced to
 incorporate multimedia and hypermedia features.  However, interest in
 ODA is perceived to be decreasing, and it is recommended that ODA
 should not form a basis for further RARE work in networked
 hypermedia.
 PREMO is a new work item in the ISO graphics standardisation
 community, which appears to overlap with MHEG and HyTime.  It is not
 clear that the PREMO work, which is at a very early stage, is
 worthwhile in view of the existence of those standards.
 Acrobat PDF is a format for representing multimedia (printable)
 documents in a portable, revisable form.  It is based on Postscript,
 and is being proposed by Adobe Inc (originators of Postscript) as an
 industry standard.  RARE should maintain awareness of this technology
 in view of its potential impact on multimedia information systems.
 There are various standards which have relevance to the way
 multimedia data is accessed across the network.  Many of these have
 been described in a previous report [1].  Two further access
 protocols are the proposed multimedia extensions to SQL, and the
 Document Filing and Retrieval protocol.  Neither of these are likely
 to have major significance for networked multimedia information
 systems.
 Other standards of importance include:
    o    MIME, a multimedia email standard which defines a range of
         media types and encoding methods for those types which are
         useful in a wider context.
    o    AVIs (Audio-Visual Interactive services) and the associated
         multimedia scripting language SMSL, which form a
         standardisation initiative within CCITT (now ITU-TSS) to
         specify interactive multimedia services which can be
         provided across telephone/ISDN networks.
 There are two important trade associations which are involved in
 standardisation work.  The Interactive Multimedia Association (IMA)
 has a Compatibility Project which is developing a specification for
 platform-independent interactive multimedia systems, including
 networking aspects.  A newly-formed group, the Multimedia
 Communications Forum (MMCF), plans to provide input to the standards
 bodies.  It is recommended that RARE become an Observing Member of
 the MMCF.  A third trade association - the Multimedia Communications
 Community of Interest - has also just been formed.

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 Future Directions
 Three common design approaches emerge from the variety of systems and
 standards analysed in this report.  They can be described in terms of
 distinctions between different aspects of the system:
    o    content is distinct from hyperstructure
    o    media type is distinct from media encoding
    o    data is distinct from protocol
 Distributed hypermedia systems are emerging from the
 research/development phase into the experimental deployment phase.
 However, the existing global information systems (Gopher, WAIS and
 WWW) are still largely limited to the use of external viewers for
 nontextual data.  The most significant mismatches between the
 capabilities of currently-deployed systems and user requirements are
 in the areas of presentation and quality of service (i.e.,
 responsiveness).
 Improving QOS is significantly more difficult than improving
 presentation capabilities, but there are a number of possible ways in
 which this could be addressed.  Improving feedback to the user,
 greater multi-threading of applications, pre-fetching, caching, the
 use of alternative "views" of a node, and the use of isochronous data
 streams are all avenues which are worth exploring.
 In order to address these problems, it is recommended that RARE seek
 to adapt and enhance existing tools, rather than develop new ones.
 In particular, it is recommended that RARE select the World-Wide Web
 to concentrate its efforts on.  The reasons for this choice revolve
 around the flexibility of the WWW design, the availability of
 hyperlinks, the existing effort which is already going into
 multimedia support in WWW, the fact that it is an integrating
 solution incorporating both WAIS and Gopher support, and its high
 rate of growth compared to Gopher (despite Gopher's wider
 deployment).  Gopher is the main competitor to WWW, but its
 inflexibly hierarchical structure and the absence of hyperlinks make
 it difficult to use for highly-interactive multimedia applications.
 It is recommended that RARE should invite proposals for and
 subsequently commission work to:
    o    Develop conversion tools from commercial multimedia
         authoring packages to WWW, and accompanying authoring
         guidelines.

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    o    Implement and evaluate the most promising ways of overcoming
         the QOS problem.
    o    Implement a specific user project using these tools, to
         validate that the facilities being developed are truly
         relevant to real applications.
    o    Use the experience gained to inform and influence the
         development of the WWW technology.
    o    Contribute to the development of PC/MS Windows and Apple
         Macintosh WWW clients, particularly in the multimedia data
         handling area.
 It is noted that the rapid growth of WWW may in the future lead to
 problems through the implementation of multiple, uncoordinated and
 mutually incompatible add-on features.  To guard against this trend,
 it may be appropriate for RARE, in coordination with CERN and other
 interested parties such as NCSA, to:
    o    Encourage the formation of a consortium to coordinate WWW
         technical development.

1. Introduction

1.1. Background

 This study was inspired by the realisation that while some aspects of
 distributed multimedia technology are being actively introduced into
 the European research community (for instance, audiovisual
 conferencing, through the MICE project), other aspects are receiving
 less attention.  In particular, one category in which there seems to
 be relatively little activity is providing solutions to ease remote
 access to multimedia resources (for instance, accessing stored
 audio/video clips or images, or indeed entire multimedia
 applications, across the network).  Few commercial products address
 this, and the relevance of existing standards in this area is
 unclear.
 Of the 50 or so research projects documented in the recent RARE
 distributed multimedia survey [1], only about six have a direct
 relevance to this application area.  Where stated in the survey, the
 main research effort in these projects is often directed towards the
 "difficult" problems, such as the transfer of isochronous data and
 the design and implementation of object-oriented multimedia
 databases, rather than towards user-oriented issues.

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

1.2. Terminology

 In order to discuss multimedia information systems, we need a
 consistent terminology.  The vocabulary defined below embodies some
 of the concepts of the Dexter hypertext reference model [2].  This
 model is sufficiently general to be useful for describing most of the
 facilities and requirements of the multimedia information systems
 described in this report.  (However, the Dexter model does not
 describe searchable index objects - it is not a database reference
 model.)
  anchor             An identified portion of a node.  E.g., in a text
                     node, an anchor might be a string of one or more
                     adjacent characters, while in an image node it
                     might be a rectangular area of the image.
  composite node     A node containing data of multiple media types.
  document           Often used loosely as a synonym for node.
  hyperdocument      We refer to a collection of related nodes,
                     linked internally with hyperlinks, as a
                     "hyperdocument".  Examples are a database of
                     medical images and associated text; a module
                     from a suite of teaching material; or an article
                     in a scientific journal.  A hyperdocument may
                     contain hyperlinks to other data which exists in
                     internally with hyperlinks, as a
                     "hyperdocument". Examples are a other
                     hyperdocuments, but can be viewed as largely
                     self-contained.  It is a highlevel "unit of
                     authoring", but is not necessarily perceived as
                     a distinct unit by a reader (although it may be
                     so perceived, particularly if it contains few
                     hyperlinks to outside entities).
  hyperlink          Set of one or more source anchors and one or
                     more target anchors.  Also known simply as a
                     "link".

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  isochronous (adjective) Describes a continuous flow of data which
                     is required to be delivered by the network under
                     critical time constraints.
  leaf node          A node which contains no source anchors.
  media type         An attribute of data which describes the general
                     nature of its expected presentation.  The value
                     of this attribute could be one of the following
                     (not exhaustive) list:
                     o Text
                     o Sound
                     o Image (e.g., a "photograph")
                     o Graphics (e.g., a "drawing")
                     o Animation (i.e., moving graphics)
                     o Movie (i.e., moving image)
  monomedia (adjective)   Said of data which is all of the same media
                     type.
  multimedia (adjective)  Said of data which contains different media
                     types.  This definition is stricter than general
                     usage, where "multimedia" is often  used as a
                     generic term for non-textual data, and where it
                     may even be used as a noun.
  physical media     Magnetic or optical storage.  Not to be confused
                     with media type!
  [simple] node      A monomedia object which may be retrieved and
                     displayed as a single unit.
  source anchor      An anchor which may be "actioned" by the user,
                     causing the node(s) containing the target
                     anchor(s) in the same hyperlink to be retrieved
                     and displayed.  This process is called
                     "traversing the link".
  target anchor      an anchor forming part of a hyperlink, whose
                     containing node is retrieved and displayed when
                     the hyperlink is traversed.

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2. User Requirements

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

2.1. Applications

 Awareness of the range of networked multimedia applications which are
 currently being envisaged by computer users in the academic and
 research community leads to a better understanding of the technical
 requirements.  This section outlines some projects which require
 remote access to multimedia information across research networks, and
 which are currently either at a preliminary stage or underway.  The
 projects are divided into broad categories according to their
 characteristics.
 Multimedia Databases
 Here are several examples of multimedia projects which have a
 "database" character.
 The Peirce Telecommunity Project
    This project centres on the construction of a multimedia (text and
    image) database of the works of the American philosopher Peirce,
    together with tools to process the data and to make it available
    over the Internet.  A sub-project at Brown University focuses on
    adapting existing client/server network tools for this purpose.
    The requirements for network access include facilities for
    structured viewing, intelligent retrieval, navigation, linking,
    and annotation, as well as for domainspecific processing.
 Museum Object Databases
    The RAMA (Remote Access to Museum Archives) project is funded
    under the EEC RACE II programme.  Its objective is to develop a
    system which allows museums to make multimedia information about
    their exhibits and archived material available over an ISDN
    network.  The requirements capture and technical architecture
    design phases are now complete, and a prototype system will be
    delivered in June 1993 to link the Ashmolean Museum (Oxford, GB),
    the Musee d'Orsay (Paris, FR) and the Museum Archeological
    National (Madrid, ES).  Image data is the main media type of
    interest, although video and sound may also play a part.

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 The Bristol Biomedical Videodisk Project
    The Bristol Biomedical Videodisc is a collection of Medical,
    Veterinary and Dental images.  The collection holds some 24,000
    still images and is continuously growing.  Textual information
    regarding the images is included as part of the database and this
    can be searched on any keyword, number or other data type, or a
    combination of any of these.  The images are currently delivered
    in analogue form on a videodisc, but many institutions are unable
    to afford the cost of videodisc players.  Investigations into
    making this image and text database available across the network
    are underway.
 ArchiGopher
    ArchiGopher is a Gopher server at the College of Architecture,
    University of Michigan, dedicated to the dissemination of
    architectural knowledge.  Presently in its infancy, ArchiGopher is
    intended to become a multimedia resource for all architecture
    faculty and students world-wide.  Some of the available or planned
    resources are:
          o The College's image bank.
          o The CAD group's collection of computer models (already
            started).
          o The Doctoral Program's recent dissertation proposals and
            abstracts.
          o Example archive of Kandinsky paintings.
          o Images of 3D CAD projects.
    The principal media type in ArchiGopher is image.  Files are
    stored in both TIFF and GIF format.
 Vatican Library Exhibit
    In January 1993, the US Library of Congress mounted an electronic
    version of the exhibition ROME REBORN:  THE VATICAN LIBRARY AND
    RENAISSANCE CULTURE.  The exhibition was subsequently processed by
    the University of Virginia Library. The text files were broken
    into individual captions associated directly with each image and a
    WAIS-searchable version of the object index generated.  This has
    been made available on Gopher by the University of Virginia
    Library.

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    This project is particularly interesting, as it demonstrates some
    limitations of the Gopher system.  The principal media types are
    image and text, and it is difficult to associate a caption with
    its image - each must be fetched separately, and using the XMosaic
    or xgopher client software it is not possible to tell which menu
    entry is the image and which the caption. (This may be a
    consequence of how the data has been configured for the Gopher
    server; if so, a requirement for better publishing tools may be
    indicated.)  Furthermore, searching the object index will result
    in a Gopher menu containing references to catalogue entries for
    relevant exhibits, but not to the online images of the exhibits
    themselves, which severely limits the usefulness of the index.
    It is interesting to note that during the preparation of this
    report, the Vatican Exhibition has been mounted on the WorldWide
    Web (WWW).  The hypermedia presentation on the Web is very much
    more attractive to use than the Gopher version.
 Jukebox
    Jukebox is a project supported by the EEC libraries program.  The
    project aims to evaluate a pilot service providing library users
    with on-line access to a database of digital sound recordings.
    The database will support multi-user access and use suitable
    storage media to make available sound recordings in a compressed
    format.  Users will access the service with a personal computer
    connected to a telematic network.
 Scientific Publishing
 There are several refereed electronic academic journals presently
 distributed on the Internet.  These tend to be text-only journals,
 and have not really addressed the issues of delivering and
 manipulating non-text data.
 Many scientific publishers have plans for electronic publishing of
 existing academic journals and conference proceedings, either on
 physical media or on the network.  The Journal of Biological
 Chemistry is now published on CD-ROM, for instance.  Some publishers
 view CD-ROM as an interim step to the ultimate goal of making
 journals available on-line on the Internet.
 The main types of non-text data which are envisaged are:
    o    Images.  In many cases, image data (a microphotograph, say)
         is central to an article.  Software which recognises that
         the text may be of secondary importance to the image is
         required.

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    o    Application-specific data.  The ChemLab and MoleculeLab
         applications are widely used, and the integration of
         corresponding data types with journal articles will enhance
         readers' ability to visualise molecular structures.
         Similarly, mathematics appearing in scientific papers could
         be represented in a form suitable for processing by
         applications such as Mathematica.  Mathematical content
         could then become a much more interactive and dynamic aspect
         of research publications.
    o    Tabular data.  The ability for a reader to extract tabular
         data from a research paper, to produce a graphical
         representation, to subset the data, and to further process
         it in a number of different ways, is viewed as an essential
         part of scientific electronic publishing.
    o    Movies.  The American Astronomical Society regularly
         publishes videos to go with its academic journals.
         Electronic publishing can improve on this "hard copy"
         publishing by integrating video data much more closely with
         the source article.
    o    Sound.  There is perhaps slightly less demand for audio
         information in scientific publishing, but the requirement
         does exist in particular specialities (such as acoustics and
         zoology journals).
 Access to academic journals using at least four different paradigms
 is envisaged.  Hierarchical access, perhaps using a traditional
 journal/volume/issue/article model, is perhaps the most obvious.
 Keyword searching (or full-text indexing) will be required.  Browsing
 is another useful and often underestimated access model - to support
 browsing it is essential that "eye-catching" data (unlikely to be
 textual) is prominently accessible. The final method of access is
 perhaps the most important - the use of interactive viewing tools.
 Such tools would enable navigation of hypermedia links within and
 between articles, with gateways to special-purpose applications as
 described above.  The use of these disparate access methods implies
 more than one structure being applied to the same underlying data.
 Standards, particularly SGML, are becoming important to publishers,
 and it is clear that the SGML-based HyTime standard will be a front
 runner in providing the kind of hypermedia facilities which are being
 envisaged.  However, progress towards a common SGML Document Type
 Definition (DTD) for scientific articles, even within individual
 publishing houses and for text-only documents, is slow.

Adie [Page 16] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 17] RFC 1614 Network Access to Multimedia Information May 1994

 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.

Adie [Page 18] RFC 1614 Network Access to Multimedia Information May 1994

    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

Adie [Page 19] RFC 1614 Network Access to Multimedia Information May 1994

 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.

Adie [Page 20] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 21] RFC 1614 Network Access to Multimedia Information May 1994

         (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.)

Adie [Page 22] RFC 1614 Network Access to Multimedia Information May 1994

 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).

Adie [Page 23] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 24] RFC 1614 Network Access to Multimedia Information May 1994

      o NeXT
      o VM/CMS
      o VMS
      o OS/2
      o MVS/XA
 Servers are available for systems such as:
      o UNIX
      o VMS
      o Apple Macintosh
      o VM/CMS
      o MVS
      o MS DOS
 Gopher was developed at the University of Minnesota.
 Gopher User Image
 A Gopher client offers an interface into "gopherspace", which appears
 to the user as a hierarchy of menus and document nodes, similar in
 some ways to a file system hierarchy of directories and files.
 Selecting an entry from a menu node causes a further menu to appear,
 or causes a document to be retrieved and displayed.
 As well as "ordinary" document nodes, Gopher has "search nodes" when
 one of these is selected from a menu, the user is prompted for one or
 more words to search on.  The result of the search is a "virtual"
 menu, containing entries for document nodes (within some subset of
 gopherspace) which match the search.  A special type of Gopher search
 server called "veronica" provides access to a database of all
 directory nodes in gopherspace.  This allows a user to construct a
 virtual menu of all Gopher menu items containing a particular word.
 WAIS databases may also be located at Gopher search nodes, since some
 Gopher servers understand the format of WAIS index files.

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 Gopher Protocol
 Gopher uses a client-server paradigm.  The Gopher protocol runs over
 a reliable data stream service, typically TCP, and is fully defined
 in RFC 1436.  The following paragraphs give an overview which is
 sufficient for understanding how multimedia data is handled in
 Gopher.
 A Gopher client opens a TCP connection to a Gopher server (defined by
 machine name and TCP port number), and sends a line of text known as
 the "selector" to request information from the server.  The server
 responds with a block of data, and then closes the connection.  No
 state is retained by the server.  A null (empty) selector tells the
 Gopher server to return its "root" menu node, containing pointers to
 other information in gopherspace.
 A menu is returned from a Gopher server as a sequence of lines of
 text, each corresponding to one entry in the menu.  Each line (which
 is sometimes called a "Gopher reference") contains the following
 data, which can be used by the client software to retrieve and
 display the corresponding node in gopherspace.
    o    A single character which identifies the type of the node.
         Possible values of this type ID are given below.
    o    A human-readable string which is used by the client software
         when it displays the menu entry to the user.
    o    The selector which should be used by client software to
         retrieve the node.  It is treated as opaque by the client
         software.
    o    The domain name of the host on which the node is held.
    o    The port number to use for the TCP connection.
 A document node is sent by a Gopher server simply as lines of text
 terminated by a dot on a line by itself, or as raw binary data, with
 the end of the data indicated by the server closing the TCP
 connection.  The choice depends on the type of node.
 The currently-defined type IDs are as follows:
      0       Node is a file.
      1       Node is a directory.
      2       Node is a CSO phone book server.

Adie [Page 26] RFC 1614 Network Access to Multimedia Information May 1994

      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:

Adie [Page 27] RFC 1614 Network Access to Multimedia Information May 1994

  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>

Adie [Page 28] RFC 1614 Network Access to Multimedia Information May 1994

 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.

Adie [Page 29] RFC 1614 Network Access to Multimedia Information May 1994

 Published Non-text Data
 There is already some useful non-text data published on Gopher almost
 exclusively image data.  See for example the Vatican Library
 Exhibition at the University of Virginia Library, the ArchiGopher at
 the University of Michigan, the weather machine at the University of
 Illinois.  Some of these are described in the User Requirements
 chapter of this report.
 There seem to be rather fewer sound archives in gopherspace, but
 interested users may access the Edinburgh University Computing
 Service Gopher server on gopher.ed.ac.uk, where the Testing Area
 contains 20 or 30 short audio files in Sun audio format.  Note - the
 availability of this archive is not guaranteed.
 Advantages
 The main factor in favour of Gopher is its widespread penetration.
 There are over 1000 Gopher servers world-wide.  This popularity is
 due in part to the ease of setting up a Gopher server and making
 information available on it, particularly on a Unix platform.
 Limitations
 It is unfortunate that the relatively well-defined MIME types were
 not adopted in Gopher+.  As mentioned above, this may yet happen,
 although there appear to be reasons for keeping the set of MIME types
 small whereas Gopher requires a wide range of types to offer to
 clients.  The latest word is that the MIME registry will be expanded
 to include the types which the Gopher+ developers want.
 Gopher is inflexibly hierarchical in nature.  Hypertext or hypermedia
 it is not - links to other nodes from within document nodes are not
 possible.  There is a suggestion in the Gopher+ specification that
 alternate views of directory nodes could be used to provide some kind
 of hypermedia capability, but this does not yet exist, and it is
 unlikely that it could be made to work as easily as the WWW hypertext
 model.
 There is no access control at the user level - anyone can retrieve
 anything on a Gopher server.  There is no provision for charging for
 information.

3.2. Wide Area Information Server

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

Adie [Page 30] RFC 1614 Network Access to Multimedia Information May 1994

 available for a wide range of platforms.  Client applications are
 able to retrieve text or other media documents stored on the servers,
 by specifying keywords.  The server software searches a full-text
 index of the documents, and returns a list of documents containing
 the keywords (ranked according to a heuristic algorithm).  The client
 may then request the server to send a copy of any of the documents
 found.  Relevant documents can be fed back to a server to refine the
 search.  Successful searches can be automatically re-run, to alert
 the user when new information becomes available.
 WAIS was developed by Thinking Machines Corporation of Cambridge,
 Massachusetts, in collaboration with Apple Computer Inc., Dow Jones
 and company, and KPMG Peat Marwick.  The WAIS software has been made
 freely available; however Thinking Machines has announced that they
 will stop support for their publicly-distributed WAIS as of version
 8b5.1.  Future support and development of the publicly-distributed
 WAIS has been taken over by CNIDR (Clearinghouse for Networked
 Information Discovery and Retrieval) in the USA.  Future CNIDR
 releases will be called FreeWAIS.  A new company, WAIS Inc, has been
 formed by Thinking Machines to take over commercial exploitation of
 the Thinking Machines WAIS software.
 WAIS server software is available for the following platforms:
      o       UNIX
      o       VAX/VMS
 Client software is available for the following platforms:
      o       UNIX (versions for X, Motif, Open Look, Sun View)
      o       NeXT
      o       Macintosh
      o       MS DOS
      o       MS Windows
      o       VAX/VMS
 There are currently over 400 WAIS databases available on the
 Internet.  WAIS is also the basis of some commercial information
 services on private networks.

Adie [Page 31] RFC 1614 Network Access to Multimedia Information May 1994

 WAIS User Image
 In order to ask a question, the user must first select one or more
 databases in which to look for the answer.  (The list of all
 available databases is available from a number of well-known sites.)
 The next step is to enter one or more keywords as the basis of the
 search.  The search will return a list of documents (the "result
 set") which contain any of the keywords.  Each document is given a
 ranking (a number between 1 and 1000) which indicates how relevant to
 the user's question the server believes the document to be.  The size
 of each document is also shown in the list.  The user may limit the
 size of the result set - the default limit is typically 40 documents.
 The user may then choose to retrieve and display one or more
 documents from the list.  Alternatively, he or she may designate one
 or more documents in the list as "relevant", and perform another
 search to find "more documents like this".  This is called "relevance
 feedback".
 The user may retrieve general information about the database, and may
 examine the catalogue of all documents in the database.  There is
 also a "database of databases", which may be searched to identify
 WAIS databases which may be relevant to a subject.
 WAIS Protocol
 The user interface (client) talks to the server using an extended
 version of a standard ANSI protocol called Z39.50.  This is now
 aligned with the ISO SR (Search and Retrieval) protocol for
 bibliographic (library) applications, which is part of OSI.  The
 present WAIS protocol does not utilise a full OSI stack - APDUs are
 transferred directly over a TCP/IP connection.  The WAIS protocol is
 described in [5].
 WAIS does not, at this time, implement the full Z39.50-1992
 specification - in particular, WAIS does not permit Boolean searches
 (e.g., "find all documents containing 'chalk' and 'cheese' but not
 'green'").  However, Boolean search capability is being added to the
 FreeWAIS implementation.  There are facilities in the Z39.50 protocol
 for access control and charging, but these are not currently
 implemented in WAIS.
 The WAIS extensions to Z39.50 are mainly to provide the relevance
 feedback capability.
 Note that the Z39.50 protocol is not stateless - the result set may
 in some circumstances be retained by the server for the user to
 further refine or refer to.  However, the subset of Z39.50 used by

Adie [Page 32] RFC 1614 Network Access to Multimedia Information May 1994

 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.

Adie [Page 33] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 34] RFC 1614 Network Access to Multimedia Information May 1994

      o       NeXT
 There is server software available for:
      o       VM mainframes.
      o       UNIX
      o       Macintosh
      o       VMS
 WWW User Image
 The WWW world consists of nodes (usually called documents) and links.
 Links are connections between documents: to follow a link, a reader
 clicks with a mouse on a word in the source document, which causes
 the linked-to document to be retrieved and displayed.  (On systems
 without a mouse, the user types a number instead.)
 Indexes are special documents which, rather than being read, may be
 searched.  To search an index, a reader supplies keywords (or other
 search criteria).  The result of a search is a "virtual" document
 containing links to the documents found.  All documents, whether
 real, virtual or indexes, look similar to the reader.
 The WWW addressing mechanism means that an interface to Gopher and
 anonymous FTP information sources may be established, in a way which
 is transparent to the user.  Thus, the whole of gopherspace is part
 of the Web.  Transparent gateways to other systems, including Hyper-G
 and WAIS, are also available.
 URL
 All nodes on the Web are addressed using the "Universal [or Uniform]
 Resource Locator" (URL) syntax, defined in [6].  This is an Internet
 Draft produced by the IETF URL Working Group.
 A URL is a name for an object (which may be a document or an index)
 on the Internet.  It has the general form:
    <scheme> : <path> [ # <anchorid> ]
 The <scheme> identifies an access protocol or method for the object.
 Some of the schemes are HTTP (the native WWW protocol), anonymous
 FTP, Andrew file system, news, WAIS, Gopher.  The <path> component
 locates the document in a way significant for the access method.

Adie [Page 35] RFC 1614 Network Access to Multimedia Information May 1994

 Thus for instance for anonymous FTP, the path includes the fully
 qualified domain name of the host on which the document resides, and
 the directory and file name under which it may be found.  For some
 schemes, the <path> may include a search string (or combination of
 strings) which is used to address a "virtual" object formed by
 searching an index of some kind.  The HTTP, WAIS and Gopher schemes
 can use search strings, which usually follow the rest of the path,
 separated from it by a ?.
 The optional <anchorid> is used for addressing within an object.  Its
 interpretation is not defined in the URL specification.
 "Partial" URLs may be specified.  These are used within a document on
 the Web to refer to another "nearby" document - for instance to a
 document in another file on the same machine.  Certain parts of the
 URL (e.g., the scheme and machine name) may be omitted, according to
 well-defined rules.  This makes it much easier to move groups of
 documents around, while maintaining the links within and between
 them.
 A URL locates one and only one object on the Internet.  However, more
 than one URL may point to the same object.  Given two URLs, it is not
 in general possible to determine whether they refer to the same
 object.  Furthermore, there is no guarantee that a single URL will
 refer to the same object at different times (the object may change
 incrementally, or it may be completely replaced with something
 different, or it may indeed be removed).
 HTTP
 HTTP (HyperText Transfer Protocol) is the protocol employed between
 server and client.  It is defined in [7].  The protocol is currently
 being revised (see the Future Developments section below), and will
 eventually be proposed as an Internet standard.
 The original protocol is extremely simple, and requires only a
 reliable connection-oriented transport service, typically TCP/IP.
 The client establishes a connection with the server, and sends a
 request containing the word GET, a space, and the partial URL of the
 node to be retrieved, terminated by CR LF.  The server responds with
 the node contents, comprising a text document in the Hypertext Markup
 Language (HTML).  The end of the contents is indicated by the server
 closing the connection.

Adie [Page 36] RFC 1614 Network Access to Multimedia Information May 1994

 HTML
 HTML (HyperText Markup Language) is the way in which text documents
 must be structured if they are to contain links to other documents.
 Non-HTML text documents may of course be made available on the Web,
 but they may not contain links to other documents (i.e., they are
 leaf nodes), and they will be displayed by browsers without
 formatting, probably using a fixed-width font.  Like HTTP, HTML is
 also undergoing enhancement, but the original version is defined in
 [7], and is being submitted as an Internet draft.
 HTML is an application of SGML (Standard Generalized Markup
 Language).  It defines a range of useful tags for indicating a node
 title, paragraph boundaries, headings of several different levels,
 highlighting, lists, etc.  Anchors are represented using an <A> tag.
 For instance, here is an example of HTML containing an anchor:
 The HTTP protocol implements the WWW <A NAME=13
 HREF="../../Administration/DataModel.html">data model</A> .
 The location of the anchor is the text "data model".  It is a source
 anchor, with a target given by the URL in the HREF attribute, so the
 text would appear highlighted in some way in a client's window, to
 indicate that clicking on it would cause a hyperlink to be traversed.
 It is also a target anchor, with an anchor ID given by the NAME
 attribute.  A source anchor referring to this target would specify
 #13 at the end of the node's URL.  Traversing a hyperlink to this
 node would cause the entire node to be retrieved, but the target
 anchor text would be displayed in some emphasised way - for instance
 if the retrieved text is displayed in a scrolling window, it might be
 positioned such that the target anchor appears at the top of the
 window.
 Another attribute of the <A> element, TYPE, is also available, which
 is intended to describe the nature of the relationship modelled by
 the link.  However, this is not in extensive use, and there appears
 to be no registry of the possible values of such types.
 Future Developments
 HTTP and HTML are currently being extended in a backward-compatible
 way to add multimedia facilities.  [8] describes the HTTP2 protocol.
 The revised HTML is defined in [9].  Both documents are subject to
 change (and indeed the HTML2 specification has changed substantially
 during the preparation of this report).

Adie [Page 37] RFC 1614 Network Access to Multimedia Information May 1994

 The revised HTML contains many enhancements which are useful for
 multimedia support.  Some of the most relevant are listed below.
    o    "Universal Resource Numbers" are a proposed system for
         unique, timeless identifiers of network-accessible files
         presently being designed by IETF Working Groups.  URNs must
         be distinguished from URLs, which contain information
         sufficient to locate the document. URNs may be allocated to
         nodes and may be represented in source anchors.  This saves
         client software from retrieving a copy of something it
         already has - allowing sensible caching of large video
         clips, for instance.  The disadvantage is that when
         something is changed and given a new URN, the source anchors
         of all links which point to it must be changed (and the URNs
         of these documents must therefore be changed, and so on).
         Therefore, it makes sense to allocate URNs only to very
         large documents which change rarely, and not to the
         documents which reference them.
    o    The title of a destination document may be included as
         anattribute of a source anchor.  This allows a client to
         display the title to the user before or during retrieval,
         and also allows data which does not itself contain a title
         (e.g., image data) to be given one.
    o    There is provision for in-line non-text data (e.g., images,
         video, graphics, mathematical equations), which appears in
         the samewindow as the main textual material in the node.
    o    The concept of the relationship expressed by a hyperlink is
         expanded.  Both source and target anchors may contain
         relation attributes which point forwards and backwards
         respectively. Possible relationships include "is an index
         for", "is a glossary for", "annotates", "is a reply to", "is
         embedded in", "is presented with".  The last two are useful
         for multimedia - for instance, the "embed" relationship
         could cause a retrieved image to be fetched and embedded in
         the display of a text node, and the "present" relationship
         could cause a sound clip to be automatically retrieved and
         presented along with a text node.
 The HTTP2 protocol maintains the same stateless
 connect/request/response/close procedure as the current HTTP
 protocol.  Data is transferred in MIME-shaped messages, allowing all
 MIME data formats (including HTML) to be used.  As well as the GET
 operation, HTTP2 has operations such as:

Adie [Page 38] RFC 1614 Network Access to Multimedia Information May 1994

  HEAD               Fetch attribute information about a node
                     (including the media type and encoding)
  CHECKOUT/CHECKIN/PUT/POST
                     These allow nodes to be checked out for updating
                     and checked back in again, and new nodes to be
                     created.  New node data is supplied in MIME
                     shape with the request.
 The request from the client can contain a list of formats which the
 client is prepared to accept, user identification, authorisation
 information (a placeholder at present), an account name to charge any
 costs to, and identification of the source anchor of the hyperlink
 through which the node was accessed.
 The response from the server may contain a range of useful attributes
 (e.g., date, cost, length - but only for non-text data).  The server
 may redirect the query, indicating a new URL to use instead.  It may
 also refuse the request because of authorisation failure or absence
 of a charge account in the request.
 The protocol also contains a mechanism which is designed to allow the
 server to make an intelligent decision about the most appropriate
 format in which to return data, based on information supplied in the
 request by the client.  This may for instance allow a powerful server
 to store the uncompressed bitmap of an image, but to compress it on
 request using an appropriate encoding, according to the decoding
 capabilities announced by the client.
 An HTTP2 server and client are currently under test.  Some HTML2
 features are already fitted to the XMosaic browser.
 Mosaic
 The Mosaic project, located at the US National Centre for
 Supercomputing Applications (NCSA) at the University of Illinois, is
 developing a networked information system intended for wide-area
 distributed asynchronous collaboration and hypermedia-based
 information discovery and retrieval.  Mosaic, which is specifically
 oriented towards scientific research workers, has adopted the World
 Wide Web as the core of the system, and the first Mosaic software to
 appear was the XMosaic WWW client for UNIX with X.  Other clients of
 similar functionality are under development for the Apple Macintosh
 and the PC with Windows.
 The capabilities of the XMosaic browser include:

Adie [Page 39] RFC 1614 Network Access to Multimedia Information May 1994

    o    Support for NCSA's Data Management Facility (DMF) for
         scientific data.
    o    Support for transferring data with other NCSA tools such
         asCollage, using NCSA's Data Transfer Mechanism (DTM).
    o    The ability to "check out" documents for revision, and to
         check them back in again.
    o    Local and remote annotation of Web documents.
 Future planned functionality includes:
    o    In-line non-text data (in addition to images).
    o    Information space graphical representation and control.
    o    Hypermedia document editing.
    o    Information filtering.
 NCSA intends to make the entire Mosaic system publicly available and
 distributable.
 The XMosaic browser was used extensively for finding and retrieving
 information used to prepare this report.
 Web Publishing
 Making a web is as simple as writing a few SGML files which point to
 your existing data. Making it public involves running the FTP or HTTP
 daemon, and making at least one link into your web from another. In
 fact,  any file available by anonymous FTP can be immediately linked
 into a web. The very small start-up effort is designed to allow small
 contributions.
 At the other end of the scale, large information providers may
 provide an HTTP server with full text or keyword indexing. This may
 allow access to a large existing database without changing the way
 that database is managed. Such gateways have already been made into
 Digital's VMS/Help, Technical University of Graz's "Hyper-G", and
 Thinking Machine's WAIS systems.
 There are a few editors which understand HTML - for instance on UNIX
 and on the NeXT platform.

Adie [Page 40] RFC 1614 Network Access to Multimedia Information May 1994

 Published non-text data
 See the multimedia demo node on:
 http://hoohoo.ncsa.uiuc.edu:80/mosaic-docs/multimedia.html
 This contains links to images, sound, movies and postscript media
 types.  The media type is determined by the filename extension in the
 URL specification of the target node.  The (XMosaic) client uses this
 to invoke a separate program appropriate for displaying the media
 type, or in some cases it can be displayed embedded within the source
 document.  The latter method uses an <IMG> tag, which is part of
 HTML2.
 Advantages
 WWW is a hypertext system and its underlying technology is thus
 richer than Gopher.  The use of SGML, which is of increasing
 importance in hypermedia systems, allows a great deal of
 expressiveness and structure, and enables text to be presented in an
 attractive way.  The facilities for multimedia data in the extended
 versions of HTTP and HTML are excellent.  It also seems that QOS and
 management issues identified in Chapter 2 are to some degree catered
 for in these extensions.
 Limitations
 There is no indication in the source anchor of the media type of the
 destination node, or of its size (this has been ruled out on the
 argument that the information is likely to degrade with time).  It is
 necessary to perform a HEAD request (in HTTP2) to deduce this.
 Link source anchors must be in text documents, so non-text nodes must
 be leaf nodes.  However, with HTML2 using the <IMG> tag, an embedded
 bitmap may be used as a source anchor, and the position of the mouse
 click within the image is passed to the server, which can then choose
 to return a different document depending on where in the image the
 mouse was clicked.
 WWW is much less prevalent than Gopher, partly because of an
 (erroneous?) perception that setting up an HTTP server is more
 complex than setting up a Gopher server.  There are only about 60
 servers world-wide; however the growth in the use of WWW is much
 faster than the growth in the use of Gopher.  The availability of
 sophisticated WWW clients such as XMosaic is fuelling this growth.

Adie [Page 41] RFC 1614 Network Access to Multimedia Information May 1994

3.4. Evaluating Existing Tools

 This section compares the capabilities of the Gopher, WAIS and
 WorldWide Web systems (abbreviated as GWW) to the informal
 requirements defined in section 2.3.
 Platforms
 The table below gives the names of the most important client software
 for each of GWW on the three most important platforms of interest.
 WWW is the weakest, with clients for the Macintosh and the PC still
 under development.  The main PC Gopher client is "PC Gopher III",
 which is a DOS program, not a Windows program.
  CLIENTS      Gopher          WAIS                WWW
  Macintosh    TurboGopher     WAIStation          (No name)
                                                   (beta version
                                                   available)
  PC with      HGopher (two    WAIS for            Cello (beta
  Windows      others also     Windows, WAIS       version
               available)      Manager             available),
                                                   Mosaic (beta due
                                                   3Q93)
  UNIX with X  Xgopher,        XWAIS               XMosaic
               XMosaic
 At present, multimedia support in most of these clients (where it
 exists) is limited to the invocation of external "viewer" programs
 for particular media types.  The exception is XMosaic, which supports
 in-line images in WWW documents.
 Media Types
 The GWW tools can all handle multiple media types well.
    o    Text is very well supported by all three tools.  WWW offers
         facilities for displaying "richer" text, supporting
         headings, lists, emphasised text etc., in a standardised way.
    o    Image data is also well supported, using either external
         viewers (e.g., the TurboGopher client software on a Macintosh
         might invoke the JPEGView program to display an image); or
         in-line display within a text document (WWW with XMosaic on
         UNIX).

Adie [Page 42] RFC 1614 Network Access to Multimedia Information May 1994

    o    There is little direct support for application-specific
         data, but most systems allow data of a nominated type to be
         passed to an external viewer or editor program.  This tends
         to be a function of the client software rather than being
         built in to the protocol or server.  There has been
         discussion in the WWW community about using TeX for
         representing mathematical equations, and about providing
         "panels" within a text document where a separate application
         could render its application-specific data (or indeed any
         data which can be represented spatially).  This latter
         suggestion fits well with the OLE (Object Linking and
         Embedding) approach used in Microsoft Windows.
    o    Sound can be supported through the external "viewer"
         concept. Some platforms don't have readily-available
         "viewers" with "tape recorder"-style controls for replaying.
         There is no single commonly-accepted sound encoding format.
    o    Video data can be handled using external viewers.  MPEG and
         QuickTime are the most common encodings.
 One essential capability of a client/server protocol is the ability
 for the client to determine the type of a node (and a list of
 available encodings) before downloading it.  WAIS and Gopher transfer
 this information in the result set and menu respectively.  WWW
 clients currently determine this information either from analysing
 the URL of a target node, or by the occurrence of the <IMG> tag.  The
 new WWW HTTP2 protocol allows the media type and encoding of a node
 to be determined through a separate interaction with the server.
 The GWW systems all use different methods for expressing type and
 encoding.  WAIS does not distinguish the encoding from the media
 type.  WWW is moving to the MIME type/encoding system.  Gopher does
 not distinguish type and encoding, but Gopher+ does, and is also
 moving to the MIME type/encoding system.
 Hyperlinks
 Only the WWW system has hyperlinks.  Source anchors may be text,
 images, or points within an image.  Target anchors may be entire
 nodes of any media type, or points within (with HTTP2, portions of)
 text nodes.
 Gopher+ could potentially be enhanced to include hyperlinks, but
 there seems to be no development effort going towards this - those
 who need hyperlinking are using WWW.

Adie [Page 43] RFC 1614 Network Access to Multimedia Information May 1994

 Gopher menus can be constructed to allow alternative views of
 gopherspace.  For instance, a geographically-organised menu tree of
 gopherspace is in place, but a parallel subject-based menu tree could
 be added as an alternative way of access to the same data.  (There
 are in fact moves to set this up.)  Since WWW offers a superset of
 Gopher functionality, these comments also apply to the Web.  In fact,
 the Web already has a rudimentary subject tree.
 In both Gopher and WWW, non-textual data may be used in different
 information structures without having to maintain more than one copy.
 Presentation
 There is little support in GWW for controlling the presentation of
 non-text data.
    o    Backdrops are not supported by GWW.
    o    Buttons are supported in a limited way - typically, a node
         is retrieved by clicking on a highlighted text phrase, or on
         an entry in a list.  In XMosaic, bitmap images can be used
         as buttons. However, there is no support for different
         styles of button.  Client software may have generic
         navigation buttons (e.g., "Back", "Next", "Home") which are
         always available and don't form part of a node.
    o    Synchronisation in space is not supported by GWW, except
         that WWW supports contextual synchronisation of images using
         the <IMG> tag.
    o    Synchronisation in time is not supported by GWW.
 Searching
 WAIS supports keyword searching, and is very well suited for that
 task.  The Gopher+ protocol could potentially support multimedia
 database querying applications through the ASK attribute, but there
 is as yet no server implementation which supports such database
 applications.  In the WWW project, there are ongoing discussions on
 how best to extend HTML to cope with database query applications - an
 <INPUT> tag has been suggested - but no consensus has yet emerged.
 Both Gopher and WWW can make use of WAIS-type keyword searching:
 either by incorporating WAIS code into the server (enabling WAIS
 index files to be searched); or through WAIS gateways, which run
 searches on remote WAIS servers in response to queries from non-WAIS
 clients.

Adie [Page 44] RFC 1614 Network Access to Multimedia Information May 1994

 Interaction
 XMosaic allows users to make text (or on some platforms, audio)
 annotations to any text node.  The annotations appear at the end of
 the text display..  They are held locally - other users of the node
 do not see the annotations (but a recently added facility allows
 globally-visible annotations held on an "annotation server").  Text
 annotations may include hyperlinks to other nodes (provided the user
 knows how to use HTML).  Other clients do not provide such
 facilities.
 There is a move to add an "email" address notation to URL.  This
 would allow WWW client software to invoke a mail program when a user
 selects an anchor with such a URL.
 There are plans to allow WWW users to delineate a rectangular area of
 interest within an image for use in an HTTP request.
 There is no support in GWW clients for interacting with sequences of
 images in the way described in section 2.3.6.
 Quality of Service
 The user expectations for responsiveness mentioned in section 2.3.7
 are difficult to meet with currently-deployed wide-area network (or
 even LAN) technology, particularly for voluminous multimedia data.
 None of the GWW systems currently exploit the emerging isochronous
 data transfer capabilities of protocols such as RTP and technologies
 such as ATM.  None of them make serious attempts to alleviate the
 problem in other ways (except for WWW, which defines some mechanisms
 in HTTP2 for format negotiation based on size and available bandwidth
 considerations).
 Management
 The following table shows the support for three key management
 facilities in the GWW systems.  The first two facilities require
 support in the client/server protocol, the third requires support in
 the server, but depends on authentication being available.
                      Gopher         WAIS          WWW
  Access control      No             No1           Yes, in
  and                                              HTTP2
  authentication

Adie [Page 45] RFC 1614 Network Access to Multimedia Information May 1994

  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.

Adie [Page 46] RFC 1614 Network Access to Multimedia Information May 1994

4. Research

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

4.1. Hyper-G

 Hyper-G [10] is an ambitious distributed hypermedia research project
 at a number of institutes of the IIG (Institutes for Information-
 Processing Graz), the Computing and Information Services Centre of
 the Graz University of Technology, and the Austrian Computer Society.
 It is funded by the Austrian Ministry of Science. It combines
 concepts of hypermedia, information retrieval systems and
 documentation systems with aspects of communication and
 collaboration, and computer-supported teaching and learning.
 Unlike WWW, Hyper-G supports bi-directional links.  This enables
 users to see which other documents reference the one they are using,
 and also allows the system to avoid dangling pointers when a linkedto
 document is deleted.  Another difference from WWW is that links are
 kept separately from their source and target nodes, to allow easy
 linking of read-only documents and for ease of link maintenance.  In
 addition to manually defined links, Hyper-G supports automatic static
 and dynamic (i.e., view-time) generation and maintenance of links.
 Hyper-G has a concept of generic "structures" - an additional layer
 of relationships imposed on (and orthogonal to) the web of documents
 and links.  A document can be part of more than one structure, and
 structures may be hierarchically related.  Types of structure
 include:
    o    "Clusters" are a set of documents which are all
         presentedtogether.
    o    "Collections" are unordered sets of documents or other
         structures, and can be used as query domains or to construct
         gopher-like menus.
    o    "Paths" are ordered sets of documents or structures, which
         must be visited sequentially.
 One application of the structure concept is the provision of "guided
 tours" through the information space.
 In addition to hypernavigation, the collection hierarchy and guided
 tours, another strategy for interaction with the system is the use of
 database queries.  Two kinds of query are supported: keyword
 searching in a user-defined list of databases; and collection

Adie [Page 47] RFC 1614 Network Access to Multimedia Information May 1994

 specific form-filling queries.  In the latter case, the answer to the
 query may appear dynamically as the form is filled out.
 Four modes of user identification are supported: "identified", where
 a userid is publicly associated through name and address information
 with a particular individual; "semi-identified", where a userid is
 associated by the system with an individual, but the user is only
 known to other users through a pseudonym; "anonymously identified",
 where the userid is not associated by the system with any individual;
 and "anonymous", where there is no userid (or a generic userid such
 as "guest").  Possible operations in the system depend on the user's
 mode of identification.  Users may access the system in any desired
 mode, and switch to other modes only when necessary.
 Hyper-G contains specific support for multilingual documents and
 document clusters.  Users may specify an ordered list of preferred
 languages, for instance.  There are plans to experiment with
 automatic translation programs.
 Integration of other, external, systems such as WWW into Hyper-G in a
 seamless manner is possible.
 Hyper-G is in use as a CWIS within Graz Technical University.  Client
 software is available for UNIX workstations from DEC, HP, SGI, and
 SUN.  The system is still in an experimental state, but it has been
 used by about 200 students as part of a course on the social impact
 of information technology.

4.2. Microcosm

 Microcosm [11] is an open hypermedia system developed at the
 University of Southampton.  It is implemented on the PC under MS
 Windows, and versions for the Apple Macintosh and for UNIX with X are
 under development.
 Microcosm consists of a number of autonomous processes which
 communicate with each other by a message-passing system.  Information
 about hyperlinks between documents is stored in a link database, or
 "linkbase", and is not stored in the documents themselves.  This has
 the advantages that:
    o    Links to and from read-only documents (perhaps stored on CD-
         ROM) are possible.
    o    Documents need undergo no conversion process to be imported
         into the system - they can still be viewed and edited using
         the original application which created them, without the
         link information getting in the way.

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    o    It is as easy to establish links to and from non-text
         documents as text documents.
 In Microcosm, the user interacts with a "viewer" program for a
 particular media type.  Such programs may be specifically written for
 use with Microcosm (about 10 such viewers have been written for a
 number of common media types and encodings); or they may be a program
 adapted for use with Microcosm (the programmability of Microsoft Word
 for Windows has allowed it to be so adapted); or it may even be a
 program with no knowledge of Microcosm.
 The user selects an object (e.g., a piece of text) in the viewer, and
 requests Microcosm to perform an action with the object - typically
 to follow a link to another document.  This may involve executing
 another viewer to display the target document.
 Microcosm link source anchors may be specific (denoting a unique
 point in a particular document), local (denoting any occurrence of a
 particular object in a particular document) or generic (denoting any
 occurrence of an object in any document).  Target anchors may specify
 specific objects within a document.  Other link styles are
 textretrieval links (looking up a full-text index , as WAIS does),
 and relevance links to a set of documents using similar vocabulary to
 the source document (again, similar to WAIS's relevance feedback).
 Links may be created by readers as well as by authors.  Dynamically
 computed links may be added to the permanent linkbase for later use.
 A history of link traversal is maintained, and "guided tours" may be
 established through the system which allow the reader to stray from
 and return to the tour.
 Microcosm viewers operate by sending messages to the Microcosm
 system.  In MS Windows, these messages are transferred using DDE
 (Dynamic Data Exchange); in the Apple Macintosh version Apple Events
 are used, and sockets are used on UNIX.  For viewers which are not
 Microcosm aware, the user must transfer the selected object to the
 system clipboard before being able to follow a link from it.
 Networking support in Microcosm is currently under development.
 Components of Microcosm may be distributed to multiple machines there
 is not necessarily a concept of "client" and "server".
 There are problems with the Microcosm approach, common to systems
 which maintain link information separately from documents, and which
 use external viewers.

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    o    Documents move and change, thus invalidating links.
         Microcosm datestamps links to help to detect (but not
         correct) such problems.
    o    It is not always clear what links are available to be
         followed from a document, since the viewer program is
         unaware of the contents of the linkbase.
    o    It is not always possible to indicate the object within a
         document which is the target anchor of a link.  Many viewers
         automatically show the start of the document (e.g., a word
         processor), or perhaps the entire document (e.g., a picture
         viewer).  The user has no way of knowing which part of the
         target document the link just followed points to.
 Microcosm may be viewed as an integrating hypermedia framework - a
 layer on top of a range of existing applications which enables
 relationships between different documents to be established.
 Microcosm is currently being "commercialised".

4.3. AthenaMuse 2

 AthenaMuse 2 (AM2) is an ambitious distributed hypermedia authoring
 and presentation system under development by the AthenaMuse Software
 Consortium based at MIT.  It is based on the earlier AM1 system
 developed as part of MIT's Project Athena.  The first version of AM2
 is scheduled for January 1994, and will be "pre-commercial software",
 with a fully-commercialised version due about 6 months later.  Both
 the educational and commercial sectors are the intended market.  The
 system will initially be based on X and UNIX workstations, but
 PC/Windows will also be supported in a second phase.  Apple Macintosh
 support has a lower priority.
 The specifications of AM2 are available in [12].  Some of the key
 points are:
    o    AM2 will support import and export of application from and
         tostandard forms.  The project is watching standards such as
         HyTime, MHEG and ODA.
    o    Several "application themes", or frequently-occurring
         collections of functionality, are viewed as useful.  These
         are as follows:
         Application Theme                         Interactive?
         Presentation of multimedia data           No
         Exploration of a rich multimedia          Yes

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         environment
         Simulation of a real-world scenario       Partially
         Communication of real-time                No
         information to the user
         Authoring                                 Yes
         Annotation of material                    Yes
    o    "Interface templates" allow a multimedia application to make
         use of a common format for presenting a range of content.
         This is similar to the "backdrop" concept mentioned in
         section 2.3.4.
    o    A range of link types will be supported.
    o    Media content editors and interface/application editors for
         structuring will be provided.  A third class of editor, the
         "hypermedia notebook", will allow readers to excerpt and
         annotate media from AM2 applications.
 The project is developing multimedia network services, including the
 transmission of digital video, using a client-server paradigm.

4.4. CEC Research Programmes

 Some of the research programmes sponsored by the Commission for the
 European Community (CEC) contain apparently relevant projects. [1]
 has further details of some of these projects.
 RACE programme
 The RACE programme is outlined in [13], which should be consulted for
 further information about the projects described below.  The RACE
 programme targets the industrial, commercial and domestic sectors,
 and results are not necessarily directly applicable to the research
 and academic community.  RACE project numbers are given.
  RACE Phase I projects, which have mostly completed:
  R1038  MCPR - Multimedia Communication, Processing and
         Representation. This project developed a demonstrator
         multimedia system with communications capability for travel
         agents.
  R1061  DIMPE - Distributed Integrated Multimedia Publishing
         Environment. The project designed and implemented interim
         services for compound document handling, and defined a
         distributed publishing architecture.

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  R1078  European Museums Network. This project aimed to demonstrate
         interactive navigation through a pool of multimedia museum
         objects, using ISDN as the communications network.
  RACE Phase II projects:
  R2008  EuroBridge.
         Aims to demonstrate multi-point multimedia applications
         running over DQDB, FDDI and ATM test networks.
  R2043  RAMA - Remote Access to Museum Archives
         This project follows on from R1078.
  R2060  CIO - Coordination, Implementation and Operation of
         Multimedia Services.
         One aspect of this project is JVTOS - a "Joint Viewing and
         Teleoperation Service".  This aims to integrate standard
         multimedia applications running on a range of heterogeneous
         machines into a cooperative working environment, allowing
         individuals to view and interact with multimedia data on
         colleague's machines.
 ESPRIT Programme
 The ESPRIT research programme is outlined in [14], which should be
 consulted for further information about the projects listed below.
 ESPRIT project numbers are given.
  28     MULTOS - A Multimedia Filing System
         This project, which ran from 1985 to 1990, developed a
         client/server system for filing and retrieval of multimedia
         documents using the ODA interchange format standard (ODIF).
  5252   HYTEA - HyperText Authoring
         This project, which runs from 1991 to 1994, aims to develop
         a set of authoring tools for large and complex hypermedia
         applications.
  5398   SHAPE - Second Generation Hypermedia Application Project
         This project is developing a portable software environment
         comparable to a CASE tool intended to facilitate the
         realisation of complex hypermedia applications.

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  5633   HYTECH - Hypertextual and Hypermedial Technical
         Documentation This project, which ran from 1990-1991, was to
         assess the feasibility of hypermedia technology and to
         devise needed extensions to it in order to support
         applications dealing with technical documentation
         management.
  6586   PEGASUS - Distributed Multimedia Operating System for the
         1990s This project is aimed at the design of an operating
         system architecture for scalable distributed multimedia
         systems and the development of a validating prototype, the
         design and implementation of a distributed complex-object
         service and a global name service, the development of
         mechanisms for the creation, communication and rendering of
         fully digital multimedia documents in real time and in a
         distributed fashion, and the design and implementation of an
         application for the system: a digital TV director.
  6606   IDOMENEUS - Information and Data on Open Media for Networks
         of Users.  This project, which started January 1993, brings
         together workers in the database, information retrieval,
         networking and hypermedia research communities in the
         development of an "ultimate information machine".  It "will
         coordinate and improve European efforts in the development
         of next-generation information environments capable of
         maintaining and communicating a largely extended class of
         information on an open set of media".  Because of the close
         match between the subject of the IDOMENEUS project and the
         RARE WG-IMM, it is recommended that RARE establish a liaison
         with this project.

4.5. Other

 Some other research projects of less immediate relevance are listed
 below.  Some of these projects are described further in [1].
    o    Xanadu is a project to develop an "open, social hypermedia"
         distributed database server, incorporating CSCW features.
         It has been in existance for many years and has been funded
         by a number of companies.  The current status of this
         project is not known, and although iminent availability of
         alpha-test versions has been announced more than once, no
         software has been delivered.
    o    CMIFed [15] is an editing and presentation environment for
         portable hypermedia documents being developed at CWI,
         Amsterdam, NL. It is based on the "Amsterdam Model" of

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         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.

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5. Standards

5.1. Structuring Standards

 This section describes some of the important standards for providing
 hyperstructure to multimedia data.
 SGML
 SGML (Standard Generalized Markup Language - ISO 8879) is a
 metalanguage for defining markup notations for text.  SGML is used to
 write Document Type Definitions or DTDs, to which individual document
 instances must conform.  It finds application in a wide and
 increasing range of text processing applications.
 The relevance of SGML to distributed hypermedia systems is
 surprisingly high, mainly because of the great expressive power of
 SGML, and its ability to handle non-textual data using "external
 entities" and "notations".
    o    The World-Wide Web is an SGML application with its own DTD.
    o    The important HyTime hypermedia structuring standard (see
         below) is based on SGML.
    o    The forthcoming MHEG hypermedia structuring standard (see
         below) has an SGML encoding.
    o    SGML has been used in research hypermedia systems - for
         example Microcosm.
    o    SGML is used in some commercial hypermedia systems - for
         example DynaText.
    o    SGML is of increasing importance for academic publishing
         houses.
 It was interesting to note that at a recent (CEC-sponsored) workshop
 on Hypertext and Hypermedia standards, most of the speakers were
 conversant with and supportive of the use of SGML for such systems.
 A related standard which may become important for SGML on networks is
 SDIF (SGML Data Interchange Format - ISO 9069).  This standard
 specifies how an SGML document, which may exist in a number of
 separate files of different media types, may be encoded using ASN.1
 into a single bytestream.  The entity structure is preserved, so that
 the bytestream may be decoded by the recipient into the same set of
 files.

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 HyTime
 HyTime (Hypermedia/Time-Based Structuring Language) is a standardised
 infrastructure for the representation of integrated, open hypermedia
 documents.  It was developed principally by ANSI committee X3V1.8M,
 and was subsequently adopted by ISO and published as ISO 10744.
 HyTime is based on SGML.  It is not itself an SGML DTD, but provides
 constructs and guidelines ("architectural forms") for making DTDs for
 describing Hypermedia documents.  For instance, the Standard Music
 Description Language (SMDL: ISO/IEC Committee Draft 10743) defines a
 (meta-)DTD which is an application of HyTime.  In fact, HyTime
 started as an attempt to produce a markup scheme for music publishing
 purposes.
 HyTime specifies how certain concepts common to all hypermedia
 documents can be represented using SGML.  These concepts include:
    o    association of objects within documents with hyperlinks
    o    placement and interrelation of objects in space and time
    o    logical structure of the document
    o    inclusion of non-textual data in the document
 An "object" in HyTime is part of a document, and is unrestricted in
 form - it may be video, audio, text, a program, graphics, etc.  The
 terminology used in HyTime (and in this section) thus differs
 slightly from the terminology used in the rest of this report.  A
 HyTime object corresponds roughly to a node as defined in section
 1.2, and a HyTime document is a hyperdocument in the terminology of
 this report.
 HyTime consists of six modules, which are very briefly and
 selectively described below:
    o    Base module.  This provides facilities required by other
         modules, including a lexical model for describing element
         contents; facilities for identifying policies for coping
         with changes to a document, or traversing a link ("activity
         tracking"); and the ability to define "container entities"
         which can hold multiple data objects.  This last was added
         to the HyTime standard at a late stage, at the instigation
         of Apple Computers Inc, as a "hook" for their Bento
         specification [18].

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    o    Measurement module.  This allows for an object to be located
         in time and/or space (which HyTime treats equivalently), or
         any other domain which can be represented by a finite
         coordinate space, within a bounding box called an "event",
         defined by a set of coordinate points.  Coordinates may be
         expressed in any units (predefined units include
         femtoseconds, fortnights, millenia, angstroms, Northern feet
         and lightyears!).
    o    Location Address module.  In addition to the fundamental
         ability of SGML to identify and refer to elements, this
         module provides a special "named location address"
         architectural form which can be used to refer indirectly to
         data which spans elements, or which is located in external
         entities.  Data may also be addressed indirectly through the
         use of "queries", which return addresses of objects within
         some domain which have properties matching the query.  A
         "HyQ" notation is provided for defining the query.
    o    Hyperlinks module.  Two basic types of hyperlink are
         defined: the contextual link (clink) has two anchors, one of
         which is embedded in a document to explicitly denote the
         anchor location; and the independent link (ilink) which may
         have more than two anchors, and which does not require the
         anchors to be embedded in the document. ilinks thus allow
         hyperlink information to be maintained separately from
         document content.
    o    Scheduling module.  This specifies how events in a source
         finite coordinate space (FCS) are to be mapped onto a target
         FCS.  For instance, events on a time axis could be projected
         onto a spatial axis for graphical display purposes, or a
         "virtual" time axis as used in music could be projected onto
         a physical time axis.
    o    Rendition module.  This allows for individual objects to be
         modified before rendition, in an object-specific way.  One
         example is modification of colours in image so that it can
         be displayed using the currently-selected colour map on a
         graphics terminal, or changing the volume of an audio
         channel according to a user's requirements.
 It is not envisaged that a hypermedia application would need to use
 the entire range of HyTime facilities.  An application designer is
 able to choose appropriate HyTime architectural forms, and to add
 application-specific constraints to them.  The designer may also of
 course use non-HyTime SGML elements and attributes, but these aspects
 of the application can't be understood by a "HyTime engine".  Even in

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 the absence of a HyTime engine, the HyTime architectural forms
 provide a useful base of ideas from which a hypermedia system
 designer may wish to work.
 The role of a HyTime engine is not specified in the standard, but
 essentially it is a (sub)program which recognises HyTime constructs
 in document instances and performs application-independent processing
 on them.  For instance, it could interact with multimedia network
 servers to resolve and access hyperlink anchors.  A commercial HyTime
 engine (HyMinder) is under development by TechnoTeacher in the US,
 and the Interactive Multimedia Group at the University of
 Massachusetts - Lowell (contact lrutledg@cs.ulowell.edu) is also
 working on a HyTime engine (HyOctane).
 The Davenport group (a loose consortium of interested companies and
 individuals) is producing a series of standards on hypermedia which
 further constrain the HyTime architectural forms.  One example is the
 SOFABED module [19], which standardises the representation of certain
 kinds of navigational information - tables of contents, indexes and
 glossaries.
 HyTime was envisaged as an interchange format rather than as a format
 for directly-executable hypermedia applications.  It is therefore
 very expressive, but may be difficult to optimise for run-time
 efficiency.
 An attempt has been made [20] to adapt the hyperlink structure in
 WWW's existing HTML DTD to comply with HyTime's clink architectural
 form.  This requires changes to WWW document instances as well as to
 browser software, and in the absence of any immediate benefit it has
 found little favour with the WWW community.  However, it is possible
 that HTML2 will use some aspects of HyTime.
 It is recommended that any further RARE work on networked hypermedia
 should take account of the importance of SGML and HyTime.
 MHEG
 MHEG stands for the Multimedia and Hypermedia information coding
 Experts Group, also known as ISO/IEC JTC1/SC29/WG12 (it used to come
 under SC2).  This group is developing a standard "Coded
 Representation of Multimedia and Hypermedia Information Objects" (ISO
 CD 13522, or CCITT T.171), commonly called MHEG.  The standard is to
 be published in two parts - part 1 being the base notation,
 representing objects using ASN.1, and part 2 being an alternate
 notation which uses SGML.  Part 1 has nearly (June 1993) achieved CD
 status, and is intended to reach full IS in 1994.  Part 2 is intended
 to reach the CD stage in late 1993.

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 MHEG is suited to interactive hypermedia applications such as on-line
 textbooks and encyclopaedia.  It is also suited for many of the
 interactive multimedia applications currently available (in
 platformspecific form) on CD-ROM.  MHEG could for instance be used as
 the data structuring standard for a future home entertainment
 interactive multimedia appliance.  Telecommunications operators are
 interested in MHEG for providing interactive multimedia services
 across ISDN.
 To address such markets, MHEG represents objects in a non-revisable
 form, and is therefore unsuitable as an input format for hypermedia
 authoring applications: its place is perhaps more as an output format
 for such tools.  MHEG is thus not a multimedia document processing
 format - instead it provides rules for the structure of multimedia
 objects which permits the objects to be represented in a convenient
 "final" form with the aim of direct presentation.
 The MHEG draft standard is expressed in object-oriented terms.  The
 main object classes are outlined briefly below.
    o    Content class.  A content object contains the encoded
         (monomedia) information to be presented, along with
         attributes which identify the type of information and the
         encoding method, and mediaspecific attributes such as fonts
         used, sampling rate, image size, etc.
    o    Selection class and Modification class.  The user may
         interact with MHEG objects which inherit interactive
         behaviour from these classes.  (The MHEG object model
         supports multiple inheritance.)
    o    Action class.  Two types of action may be applied to
         objects: projection, which controls how objects are
         rendered; and status actions which affect the state of
         objects.
    o    Link class.  MHEG hyperlinks connect a "start" object with
         one or more "end" objects.  Links consist of a set of
         conditions relating to the state of the start object, and a
         set of actions which are carried out when these conditions
         are satisfied.  Links also define the spatio-temporal
         relationships between objects.
    o    Script class.  Script objects are used to describe more
         complex interobject linkages (e.g., multiple-source links).
         MHEG does not define a scripting language - instead it
         provides a formalism for encapsulating scripts which may be
         executed by an external program (see SMSL below).

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    o    Composite class.  Related objects may be grouped together
         into a single composite object (recursively).  The
         relationships between content objects within a composite
         object are determined by link and script objects which also
         are members of the composite object.
    o    Descriptor class.  Descriptor objects contain general
         information about sets of interchanged objects, so that a
         target system can ensure it has adequate resources to run
         the hypermedia application represented by the object set.
 The relationship between HyTime and MHEG has not yet been fully
 established.  One possible relationship [21] is that an MHEG
 application could be the output of a compilation process which used
 an equivalent HyTime document as input.  This approach would benefit
 both from the expressive power of HyTime and the run-time efficiency
 of MHEG.  However, it has yet to be shown that this is feasible,
 since the capabilities of HyTime and MHEG do not completely overlap.
 There seems to be relatively little interest in or awareness of MHEG
 within the Internet community, which is only just beginning to be
 aware of HyTime.  In view of the draft nature of the MHEG standard,
 this report recommends that RARE should not invest substantial effort
 in MHEG at this time.  However, particularly in view of the interest
 in it shown by PTTs, a watching brief should be kept on MHEG, as it
 may well be relevant in the future.
 ODA
 The Open Document Architecture standard (ODA - ISO 8613 or T.140) is
 a compound document interchange format designed for transferring
 documents between open systems.  It is able to represent documents in
 both a formatted form and a processable (i.e., revisable) form, thus
 allowing both the content and the printed appearance of the document
 to be unambiguously transferred.
 In addition to text data, ODA supports graphics and image data.  A
 revised version to be published in 1993 will support colour.  Future
 developments include support for audio content (underway) and video
 content (planned).  An interface to MHEG is also planned.
 ODA differs from SGML in that the former concerns itself with the
 physical appearance of the document, while SGML deliberately avoids
 doing so.  SGML concerns itself with semantic markup, and can be used
 to describe a wide range of data and document architectures.  ODA has
 a more limited concept of a document.

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 Hypermedia extensions to ODA (HyperODA) are underway.  The extensions
 will support:
    o    References to data held externally to the document (similar
         to SGML's external entities?).
    o    Non-linear structures, using contextual and independent
         hyperlinks based on the HyTime model.
    o    Temporal relationships between document components (e.g.,
         sequential, parallel, cyclic, duration, start delay).
 HyperODA is not being developed in competition to HyTime or MHEG its
 purpose is to add hypermedia features to ODA rather than to be a
 completely general framework for hypermedia applications.
 Bearing in mind that:
    o    the HyperODA extensions are still under development;
    o    in some senses ODA can be seen as a competitor to SGML,
         which has greater presence in the hypermedia world;
    o    there seems to be a lack of enthusiasm for ODA in the
         Internet community (the IETF WG on piloting ODA has
         disbanded);
    o    Adobe's newly-released Acrobat technology (described below)
         will have a significant effect on the marketplace;
 this report recommends that ODA should not form a basis for
 investment in networked hypermedia technology by RARE.
 PREMO
 PREMO (Presentation Environment for Multimedia Objects) is a new work
 item in ISO/IEC JTC1/SC24 (the graphics standards subcommittee).  An
 initial draft [22] exists, and the schedule calls for a CD by June
 1994, a DIS by June 1995, and the final IS by June 1996.
 PREMO addresses the construction of, presentation of, and interaction
 with multimedia objects.  It specifies techniques for creating
 audiovisual interactive single and multiple media applications.  It
 is consistent with the principles of the Computer Graphics Reference
 Model (CGRM, ISO 11072), and is defined in object-oriented terms.
 It is not clear how PREMO relates to HyTime and MHEG.  Although these
 standards are listed in section 2 (References) of the initial draft,

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 they appear not to be mentioned in the text.  The wisdom of
 developing what appears to be yet another structuring standard for
 multimedia data is doubtful.
 The PREMO work is not sufficiently advanced to permit a judgement of
 its usefulness in satisfying the requirements under discussion.
 Acrobat
 Adobe, Inc. has introduced a new format called Acrobat PDF, which it
 is putting forward as a potential de facto standard for portable
 document representation.  Based on the Postscript page description
 language, Acrobat PDF is also designed to represent the printed
 appearance of a document (which may include graphics and images as
 well as text.  Unlike postscript however, Acrobat PDF allows data to
 be extracted from the document.  It is thus a revisable format.  It
 includes support for annotations, hypertext links, bookmarks and
 structured documents in markup languages such as SGML.  PDF files can
 represent both the logical and the formatting structure of the
 document.
 Acrobat PFD thus appears to offer very similar functionality to ODA.
 Adobe's successful Postscript de facto standard profoundly influenced
 information technology - it is possible that if successful, Acrobat
 PDF will be almost as important.  RARE should be aware of this
 technology and its potential impact on multimedia information
 systems.

5.2. Access Mechanisms

 This section describes some standards which are useful in providing
 network access to multimedia data.  Of course, there are many
 multimedia transport protocols, which this report does not attempt to
 describe (see [1] for further information).  The protocols mentioned
 below are search/retrieve protocols which were not mentioned in [1].
 Multimedia Extensions to SQL
 A new work item in ISO (ISO/IEC JTC1 N2265) to extend the SQL
 standard to include multimedia data is expected to be approved
 shortly.  Initially this work will concentrate on developing a
 framework, and on free text data.  Support for non-text data will be
 added later, using a separate part of the standard for each media
 type.
 The expected timescale for this standardisation work is lengthy (part
 1 - the framework - is targeted for completion in 1996).

Adie [Page 62] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 63] RFC 1614 Network Access to Multimedia Information May 1994

 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:

Adie [Page 64] RFC 1614 Network Access to Multimedia Information May 1994

  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

Adie [Page 65] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 66] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 67] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 68] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 69] RFC 1614 Network Access to Multimedia Information May 1994

 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.

Adie [Page 70] RFC 1614 Network Access to Multimedia Information May 1994

    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.

Adie [Page 71] RFC 1614 Network Access to Multimedia Information May 1994

 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

Adie [Page 72] RFC 1614 Network Access to Multimedia Information May 1994

         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.

Adie [Page 73] RFC 1614 Network Access to Multimedia Information May 1994

         It is neither envisaged that Gopher will go away, nor that
         it won't be used for multimedia data.  However, Gopher is
         unlikely to be used for more sophisticated multimedia
         applications such as academic publishing, interactive
         multimedia databases and CAL, because of the above-mentioned
         limitations.
    o    WAIS is a specialised tool, and will certainly form part of
         the overall solution, particularly for database-type
         applications.  It is not a general solution for distributed
         hypermedia applications.
    o    AthenaMuse 2 is commercially-oriented: it is clear that
         academic and research users will have to pay to use the
         software.  Its level of use is thus very unlikely to be as
         great as publiclyavailable systems such as WWW.  Moreover,
         it does not support all the required platforms.
    o    Microcosm network support is still in early stages, limited
         at present to the PC/Windows platform.  If it can be shown
         to perform adequately over a network, if it is capable of
         scaling to global levels, and if the advantages of
         maintaining link information separately from documents are
         found clearly to outweigh the consequent difficulties, it
         may become important in the future. Microcosm's authors need
         to ensure that the commercialisation of Microcosm does not
         hinder its adoption by the academic community.
    o    Hyper-G is more difficult to dismiss.  It is still in a
         relatively early stage of development, but appears to have
         many of the necessary features.  Its main disadvantages are:
         (a) the lack of penetration outside the University of Graz -
         the author is aware of only one other site using it; and (b)
         it is currently limited to UNIX only.  The author believes
         that, given WWW's head start in terms of deployment, and the
         current progress in adding multimedia facilities to it, WWW
         stands a much better chance than Hyper-G of being accepted
         as the de facto standard for distributed multimedia
         applications on the Internet.
 Directions for RARE
 Earlier in this report, it was noted that the most important areas
 where effort was needed were (a) provision of facilities for the
 integrated presentation of multimedia data (including synchronisation
 issues); and (b) ensuring adequate responsiveness.

Adie [Page 74] RFC 1614 Network Access to Multimedia Information May 1994

 Bearing this in mind, it is recommended that RARE should invite
 proposals and (subject to funding being available) subsequently
 commission work to:
    1.   Develop conversion tools from commercial authoring packages
         to WWW, and establish authoring guidelines for authors who
         wish to use the conversion tools.  This is a significant and
         high-profile development aimed at enabling sophisticated
         multimedia applications to run over the network.  (Authoring
         guidelines will be necessary to enable authors to fit in
         with the Web's way of doing things, and to document features
         of the authoring package which should be avoided because of
         conversion difficulties.)
    2.   Implement and evaluate the most promising ways of overcoming
         the QOS problem.  This is an essential task without which
         interactive distributed multimedia applications cannot
         become a reality.  Some possibilities have already been
         outlined in the preceding chapter.
    3.   Implement a specific user project using these tools, in
         order to validate that the facilities being developed are
         truly relevant to actual user requirements.  It may be that
         partner funding from the selected user project would be
         appropriate.
    4.   Use the experience gained from 1, 2 and 3 to inform and
         influence the further development of HTML2 and HTTP2 to
         ensure that they provide the required facilities.
    5.   Contribute to the development of the WWW clients
         (particularly the Apple Macintosh and PC/MS Windows clients)
         in terms of their multimedia data handling facilities.
 Although it is strictly speaking outside the remit of this report
 (since it is not specifically concerned with multimedia data), it is
 noted that the rapid growth of WWW may in the future lead to problems
 through the implementation of multiple, uncoordinated and mutually
 incompatible add-on features.  To guard against this trend, it may be
 appropriate for RARE, in coordination with CERN and other interested
 parties such as NCSA, to:
    6.   Encourage the formation of a consortium to coordinate WWW
         technical development (protocol enhancements, etc).

Adie [Page 75] RFC 1614 Network Access to Multimedia Information May 1994

7. References

    [1]         "A Survey of Distributed Multimedia Research,
                Standards and Products", ed. C. Adie, January 1993
                (RARE Technical Report 5).
                URL=ftp://ftp.ed.ac.uk/pub/mmsurvey/
    [2]         "The Dexter Hypertext Reference Model", F. Halasz and
                M. Schwartz, NIST Hypertext Standardisation Workshop,
                January 1990.
    [3]         "Response Time and Display Rate in Human Performance
                with Computers", B. Shneiderman, Comp. Surveys 16,
                1984.
    [4]         "Gopher+: Proposed Enhancements to the Internet
                Gopher Protocol", B. Alberti, F. Anklesaria, P. Linder,
                M. McCahill, D. Torrey, Summer 1992.
                URL=gopher://boombox.micro.umn.edu:70/11/gopher/gop
                her_protocol/Gopher%2b
    [5]         "WAIS Interface Protocol", F. Davies, B. Kahle, H.
                Morris, J. Salem, T. Shen, R. Wang, J. Sui and M.
                Grinbaum, April 1990.
                URL=ftp://quake.think.com/wais/doc/protspec.txt
    [6]         "Uniform Resource Locators", T. Berners-Lee, March
                1993.  URL=ftp://info.cern.ch/pub/ietf/url4.ps
    [7]         "The HTTP Protocol as Implemented in W3", T. Berners-
                Lee, January 1992.
                URL=ftp://info.cern.ch/pub/www/doc/http.txt
    [8]         "Protocol for the Retrieval and Manipulation of
                Textual and Hypermedia Information", T. Berners-Lee,
                1993.  URL=ftp://info.cern.ch/pub/www/doc/httpspec.ps
    [9]         "Hypertext Markup Language (HTML)", T Berners-Lee,
                March 1993. URL=ftp://info.cern.ch/pub/www/doc/html-
                spec.ps
    [10]        "Hyper-G: A Universal Hypermedia System", F. Kappe and
                N. Sherbakov, March 1992. URL=ftp://iicm.tu-
                graz.ac.at/pub/HyperG/doc/report333.txt.Z

Adie [Page 76] RFC 1614 Network Access to Multimedia Information May 1994

    [11]        "Towards an Integrated Information Environment with
                Open Hypermedia Systems", H. Davis, W. Hall, I. Heath,
                G. Hill, Proceedings of the ACM Conference on
                Hypertext, Milan 1992, p181-190.
    [12]        "The AthenaMuse 2 Functional Specification", L.
                Bolduc, J. Culbert T. Harada, J. Harward, E.
                Schlusselberg, May 1992.
                URL=ftp://ceci.mit.edu/pub/AM2/funcspec.txt.Z
    [13]        "Research and Technology Development in Advanced
                Communications Technologies in Europe: RACE '92",
                CEC, March 1992.  Available from:
                raco@postman.dg13.cec.be
    [14]        "Esprit Programme Synopses", CEC, October 1992.  In
                seven volumes.  Available from
                esprit_order_mailbox@eurokom.ie
    [15]        "CMIFed: A Presentation Environment for Portable
                Hypermedia Documents", G. van Rossum, J. Jansen, K. S.
                Mullender, D. C. A. Bulterman, Amsterdam 1993 (also
                presented at ACM Multimedia 93 conference).
                URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9305.ps.Z
    [16]        "The Amsterdam Hypermedia Model: extending hypertext
                to support real multimedia", L. Hardman, D. C. A.
                Bulterman, G. van Rossum, Amsterdam 1993
                URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9306.ps.Z
    [17]        "Deja-Vu Distributed Hypermedia Application
                Framework", A. Eliens.
                URL=ftp://ftp.cs.vu.nl/eliens/Deja-Vu-proposal.ps
    [18]        "Bento Specification", J. Harris and I. Ruben, Apple
                Computer Inc, August 1992.
                URL=ftp://ftp.apple.com/apple/standards/Bento_1.0d4.1
    [19]        "Davenport Advisory Standard for Hypermedia (DASH),
                Module I: Standard Open Formal Architecture for
                Browsable Hypermedia Documents (SOFABED)", ed S. R.
                Newcomb and V. T. Newcomb.
                URL=ftp://sgml1.ex.ac.uk/davenport/sofabed.0.9.6.ps.Z
    [20]        Article in comp.text.sgml newsgroup, 24 May 1993, by
                Eliot Kimber (drmacro@vnet.ibm.com).
                URL=ftp://ftp.ifi.uio.no/SGML/comp.text.sgml/by.msg
                id/19930524.152345.29@almaden.ibm.com

Adie [Page 77] RFC 1614 Network Access to Multimedia Information May 1994

    [21]        "Emerging Hypermedia Standards" B. Markey, Multimedia
                for Now and the Future (Usenix Conference
                Proceedings), June 1991.
    [22]        "Initial Draft PREMO (Presentation Environment for
                Multimedia Objects", ISO/IEC JTC1/SC24 N847, November
                1992.
    [23]        "Recommended Practices for Multimedia Portability",
                Release 1.1 October 1990, Interactive Multimedia
                Association, 3 Church Circle, Suite 800, Annapolis,
                MD 21401-1993, USA.
    [24]        "Recommended Practices for Enhancing Digital Audio
                Compatability in Multimedia Systems", Release 3.00
                1992, Interactive Multimedia Association, 3 Church
                Circle, Suite 800, Annapolis, MD 21401-1993, USA.
    [25]        "RIFF Tagged File Format", Microsoft Inc, 1992.
    [26]        "A Vision of an Integrated Internet Information
                Service", C. Weider and P. Deutsch, March 1993,
                Work in Progress.
    [27]        "Delivering Interactive Multimedia Documents over
                Networks", S. Loeb, IEEE Communications Magazine, May
                1992.
    [28]        "A Status Report on Networked Information Retrieval:
                Tools and Groups", ed. J. Foster, G. Brett and P.
                Deutsch, March 1993.
                URL=ftp://mailbase.ac.uk/pub/nir/nir.status.report

Adie [Page 78] RFC 1614 Network Access to Multimedia Information May 1994

8. Security Considerations

 Security issues are not discussed in this memo.

9. Author's Address

 Chris Adie
 Edinburgh University Computing Service
 University Library
 George Square
 Edinburgh EH8 9LJ
 United Kingdom
 Phone: +44 31 650 3363
 Fax:   +44 31 662 4809
 EMail: C.J.Adie@edinburgh.ac.uk

Adie [Page 79]

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