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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
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2.3. Requirements Definition 19
3. Existing Systems 24
3.1. Gopher 24
3.2. Wide Area Information Server 30
3.3. World-Wide Web 34
3.4. Evaluating Existing Tools 42
4. Research 47
4.1. Hyper-G 47
4.2. Microcosm 48
4.3. AthenaMuse 2 50
4.4. CEC Research Programmes 51
4.5. Other 53
5. Standards 55
5.1. Structuring Standards 55
5.2. Access Mechanisms 62
5.3. Other Standards 63
5.4. Trade Associations 66
6. Future Directions 68
6.1. General Comments on the State-of-the-Art 68
6.2. Quality of Service 70
6.3. Recommended Further Work 71
7. References 76
8. Security Considerations 79
9. Author's Address 79
Acknowledgements
The following people have (knowingly or unknowingly) helped in the
preparation of this report: Tim Berners-Lee, John Dyer, Aydin Edguer,
Anton Eliens, Tony Gibbons, Stewart Granger, Wendy Hall, Gary Hill,
Brian Marquardt, Gunnar Moan, Michael Neuman, Ari Ollikainen, David
Pullinger, John Smith, Edward Vielmetti, and Jane Williams. The
useful role which NCSA's XMosaic information browser tool played in
assembling the information on which this report was based should also
be acknowledged - many thanks to its developers.
All trademarks are hereby acknowledged as being the property of their
respective owners.
Disclaimer
This report is based on information supplied to or obtained by
Edinburgh University Computing Service (EUCS) in good faith. Neither
EUCS nor RARE nor any of their staff may be held liable for any
inaccuracies or omissions, or any loss or damage arising from or out
of the use of this report.
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RFC 1614 Network Access to Multimedia Information May 1994
The opinions expressed in this report are personal opinions of the
author. They do not necessarily represent the policy either of RARE
or of ECUS.
Mention of a product in this report does not constitute endorsement
either by EUCS or by RARE.
Availability
This document is available in various forms (PostScript, text,
Microsoft Word for Windows 2) by anonymous FTP through the following
URL:
ftp://ftp.edinburgh.ac.uk/pub/mmaccess/
ftp://ftp.rare.nl/rare/pub/rtr/rtr8-rfc.../
Paper copies are available from the RARE Secretariat.
0. Extended Summary
Introduction
This report is concerned with issues in the intersection of
networked information retrieval, database and multimedia
technologies. It aims to establish research and academic user
requirements for network access to multimedia data, to look at
existing systems which offer partial solutions, and to identify
what needs to be done to satisfy the most pressing requirements.
User Requirements
There are a number of reasons why multimedia data may need to be
accessed remotely (as opposed to physically distributing the data,
e.g., on CD-ROM). These reasons centre on the cost of physical
distribution, versus the timeliness of network distribution. Of
course, there is a cost associated with network distribution, but
this tends to be hidden from the end user.
User requirements have been determined by studying existing and
proposed projects involving networked multimedia data. It has
proved convenient to divide the applications into four classes
according to their requirements: multimedia database applications,
academic (particularly scientific) publishing applications, cal
(computeraided learning), and general multimedia information
services.
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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.
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A specific initiative involving interested parties will be required
to formalise detailed requirements and to pilot standards in this
area. A preliminary demonstrator project, funded by publishers and
by the British Library Research and Development Department, involves
making about 30 sample scientific articles available over the
SuperJANET network, using a range of different software products. The
demonstrator project is being managed by IOP Publishing and is being
carried out at Edinburgh University Computing Service.
Existing tools, particularly WAIS and WWW, are relevant, but adequate
security and charging mechanisms are required if commercial
publishers are to use them. Many research groups are now making the
text of preprints and published research papers available on Gopher
servers.
It is interesting to note that the proceedings of the Multimedia 93
conference run by the ACM will be published electronically (on CD
ROM), using a multimedia document format designed specifically for
the event.
Computer-aided Learning
The ready availability of user-friendly multimedia authoring tools
such as AuthorWare Professional, Asymmetrix Multimedia Toolbook,
Macromind Director and many more, has stimulated much interest in
multimedia for computer-aided learning applications within the user
community. Sophisticated interactive multimedia courseware
applications are being developed in many disparate subjects
throughout the European academic community. Users are now beginning
to ask network technologists, "how can I make my multimedia
application available to others across the network?".
There is considerable interest in using the network to enhance
delivery of multimedia teaching materials - for instance to allow
students to take courses remotely (distance learning) and for their
learning process to be supported, monitored and assessed remotely.
The requirements which flow from this type of network application
include the ability to identify and authenticate the students using
the material, to monitor their progress, and to supply on-line
assessment exercises for the student to complete. Multimedia
authoring tools allow very attractive presentation environments to be
created, which encourages learning; this is viewed as essential by
course developers. Easy-to-use authoring tools (preferably existing
commercial ones) are also essential.
Finally, some learning applications involve simulations - examples
include meteorological modelling and economic simulations. Network
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delivery of teaching materials should cope with this requirement
(perhaps by acknowledging that executable scripts are just another
media type).
General Information Services
There are many other possible uses of multimedia data in networked
information servers which don't conveniently fall into any of the
above categories. Some examples are given below.
o On-line documentation. Manuals and instruction books often
rely heavily on pictorial information, and are enhanced by
dynamic media types (sound, video). The ability to access
centrally-held manuals across a network makes it much easier
to keep the information up-to-date.
o Campus-wide information systems (CWIS) are an important
growth area. The opportunities for enhancing such a
service with multimedia data (e.g., maps) is obvious.
o Multimedia news bulletins (e.g., the Internet Talk Radio,
which is sound only).
o Product information (the multimedia equivalent of paper
advertising matter).
o Consumer systems - e.g., tourist information servers. The
utility of such systems in an academic/research environment
is perhaps questionable, but it is likely that such systems
will address problems which will also be met in this
environment. We should be prepared to learn from such
projects.
2.2. Data Characteristics
Some of the characteristics which make data more appropriate for
network publication rather than publication on physical media are
listed below.
o The data may change frequently.
o Implementing corrections and improvements to the data is
very much easier.
o It is more readily available to the data user - no
purchase/delivery cycle need exist.
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o Publication on physical media may not be cost-effective for
very large volumes of data. (Of course, there is a cost in
networking the data as well, but the research/academic user
is normally insulated from this.)
o Access for large user communities can be established without
requiring each user to purchase a potentially expensive
physical media peripheral (such as a laser disk player).
This is particularly helpful in classroom situations.
o It may require less effort from the data publisher to make
data available over a network, rather than set up a manual
mechanism for distributing physical media.
o If related data from many different sources is to be
published, it may be more efficient to leave the data in
situ, and simply publish the network addresses of the data.
There are counter-reasons which may make physical media distribution
more appropriate:
o Easier to charge for. (However, charging mechanisms do
exist in some network information systems. It may be that
potential information providers need to be made more aware
of this.)
o Easier to deter or prevent copyright infringement, using
traditional copy-protection techniques.
2.3. Requirements Definition
From studying the applications described in the preceding section,
and from discussions with the people involved with the applications,
it is possible to draw up a list of general requirements which a
distributed multimedia information system for the academic and
research community should satisfy. These requirements are informally
described in the following subsections. The descriptions are
necessarily informal and incomplete: every individual application
will have its own detailed requirements, which would take a great
deal of effort to determine (and indeed some of the requirements may
not become apparent until the application is into its development
phase).
Platforms
It is clear that the European academic community, in common with
other such communities, requires support for three main platforms:
UNIX, Apple Macintosh, and PC/Windows. For multimedia client/server
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systems, the latter two are less appropriate as server platforms, but
client support for all three is vital. UNIX will be most often used
as the server platform.
There are other systems, such as VAX/VMS, which are also important in
some sectors.
Media Types
Unsurprisingly, all applications require text data to be supported as
a basic media type. Image and graphic media types are next in
importance, followed by "application-specific" data (such as tabular
scientific data, mathematical equations, chemical data types, etc).
Sound and video media types are becoming more important as users
discover how these can enhance applications.
Many different encodings are possible for each media type (e.g.,
image data can be encoded as TIFF, PCX, GIF, PICT and many more). An
information system should not constrain the type of encoding used,
and should ideally offer either a range of alternative encodings, or
conversion facilities between the stored encoding and an encoding
suitable for display by the client workstation.
Hyperlinks
It is clear that many applications require their users to be able to
navigate through the information base according to relationships
determined by the information provider - in other words, hyperlinks.
Academic publishing, CAL, on-line documentation and CWIS systems all
require this capability. The user should be able, by some action
such as clicking on a highlighted word in a text node or on a button,
to cause another node or nodes to be retrieved and displayed.
Some "hypermedia" systems are in fact simply hypertext, in that they
require the source anchor of a hyperlink to be in a text node. A
true hypermedia system allows hyperlinks to have their source anchors
in nodes of any media type. This allows a user to click the mouse on
a component of a diagram or on part of a video sequence to cause one
or more related nodes to be retrieved and displayed.
Some hypermedia systems allow target anchors of a hyperlinks to be
finer-grained than a whole node - e.g., the target anchor could be a
word or a paragraph within a text document. Without such a
capability, it is necessary for target nodes to be quite small if
precision is required in a hyperlink. This may be difficult to
manage, and fine-grained target anchors are therefore better.
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Additional structure above or orthogonal to the underlying
hyperlinked data is required in some applications. This allows the
same (generally non-textual) data to be used in several different
applications, or the implementation of different access paradigms.
Presentation
Related information of different media types must be capable of
synchronised display. Commercial multimedia authoring packages
provide many different ways of presenting, synchronising and
interacting with media elements. Some of these are summarised below.
o Backdrops. An application may present all its visual
information against a single background bitmap - e.g.,
a CAL application might use a background image of an open
textbook, with graphics, text and video data all presented
on the open pages of the book.
o Buttons. A "button" can be defined as an explicitly-
delimited area of the display, within which a mouse click
will cause an action to occur. Typically, the action will
be (or can be modelled as) a hyperlink traversal.
Applications use different styles of button - some may use
"tabs" as in a notebook, or perhaps "bookmarks" in
conjunction with the open textbook backdrop mentioned above.
Others may use plain buttons in a style conforming to the
conventions of the host platform, or may simply highlight a
word or phrase in a text display to indicate it is "active".
o Synchronisation in space. When two or more nodes are
presented together (e.g., because a link with more than one
target anchor has been traversed), the author of the
hyperdocument may wish to specify that they be presented in
a spatially-related way. This may involve: x/y
synchronisation - e.g., a video node being displayed
immediately above its text caption; it may involve
contextual synchronisation - e.g., an image being displayed in
a specific location within a text node; or it may involve z-
axis synchronisation as well - for instance a text node
containing a simple title being displayed on top of an
image, with the text background being transparent so that
the image shows through.
o Synchronisation in time. Isochronous data may require
synchronisation - the obvious case being audio and video
tracks (where these are held separately). Other examples
are: the synchronisation of an automatically-scrolling text
panel to a video clip (for subtitling); or to an audio clip
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(e.g., a translation); or synchronising an animation to an
explanatory audio track.
Searching
Database-type applications require varying degrees of sophistication
in retrieval techniques. For applications addressed in this report,
non-text nodes form the major data of interest. Such nodes have
associated descriptions, which may be plain text, or may be
structured into fields. Users need to be able to search the
descriptions, obtain a list of "hits", and select nodes from that
list to display. Searching requirements vary from simple keyword
searching, via full-text indexing (with or without Boolean
combinations of search words), to full SQL-style database retrieval
languages.
Interaction
The user must be able to annotate documents retrieved from the
information server. The annotations may be stored locally.
Similarly, the user may wish to add his own (locally-held) hyperlinks
to documents. (Actual modification of documents in the information
system itself, or shared annotations to documents - i.e., the
information system as a CSCW environment - is viewed as separate
issue which this report does not address.)
If an information provider has included contact details (such as a
mail address) in a document, it should be possible for the reader to
invoke a program (such as a mailer) which initiates communication
with the author.
In some applications, it may make sense for a user to be able to
specify a region of interest in an image or movie clip, and to
request a more detailed view of (or other information about) that
region.
Some applications require a sequence of images to be presented under
control of the user. For instance, a three-dimensional microscopic
structure could be represented as a sequence of images taken with the
microscope focused on a different plane for each image. For display,
the user could control which image was displayed using some kind of
slider control, giving the illusion of focusing a microscope. (This
particular example has been taken from the Theseus project at John
Moore's University, Liverpool, GB.)
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Quality of Service
Research has shown [3] that user toleration of delay in computer
systems depends on user perception of the nature of the requested
action. If the user believes that no computation is required,
tolerable delays are of the order of 0.2s. If the user believes the
action he or she has requested the computer to perform is "difficult"
- for instance a computation of some form - then a tolerable delay is
of the order of 2s. Users tend to give up waiting for a response
after about 20s. Networked multimedia information systems must be
able to provide this level of responsiveness.
Management
In order to support applications involving real-money information
services (e.g., academic publishing) and learning/assessment
applications, there must be a reliable and secure access control
mechanism. A simple password is unlikely to suffice - Kerberos
authentication procedures are a possibility.
Users must be able to determine the charge for an item before
retrieving it (assuming that pay-per-item will be a common paradigm
alternatives such as pay-per-call, pay-per-duration are also
possible). Access records must be kept by the information server for
charging purposes.
Learning applications have similar requirements, except that the
purpose here is not to charge for information retrieved, but to
monitor and perhaps assess a student's progress.
Scripting
Many authoring packages provide scripting languages. In most cases,
these languages are used to manage the presentation environment and
control navigation within the hypermedia document. There are other,
declarative rather than procedural, methods for achieving this, so
scripting of this type is not necessarily a requirement. However,
some application areas require executable scripts for other purposes
(e.g., simulations in CAL applications). Care in providing such a
facility is required, because of the potential for abuse (the
possibility of "trojan" scripts). However, there is work going on to
produce "safe" scripting languages - an example is "safe tcl", being
developed by Borenstein and Ousterhout (contact
ouster@cs.berkeley.edu).
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Bytestream Format
For the easy transfer and handling of a hyperdocument, it must be
capable of being encoded into a bytestream form, in such a way that
the structure of the document is preserved and it can be decoded
without loss of information.
This facility makes it possible for such documents to be supplied to
a user over electronic mail, in such a way that he or she can browse
them at his or her own site. This may be appropriate where the user
does not have a direct connection to the Internet. It will also be
useful for printing the hyperdocument.
Authoring
It is essential that a multimedia information system should have
adequate authoring tools which make it easy to prepare and publish
hypermedia information. Such tools need similar power to existing
commercial multimedia authoring software for stand-alone multimedia
applications.
3. Existing Systems
This chapter describes some existing distributed information systems
in sufficient detail to reveal how they handle multimedia data, and
analyses how well they meet the requirements outlined in the
preceding chapter.
3.1. Gopher
The Internet Gopher is a distributed document delivery service. It
allows a neophyte user to access various types of data residing on
multiple hosts in a seamless fashion. This is accomplished by
presenting the user with a hierarchical arrangement of nodes and by
using a client-server communications model. The Gopher server
accepts simple queries, and responds by sending the client a node
(usually called a document in this context).
Client software is available for a large number of systems,
including:
o UNIX (character terminals)
o X windows
o Apple Macintosh
o MS DOS
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o NeXT
o VM/CMS
o VMS
o OS/2
o MVS/XA
Servers are available for systems such as:
o UNIX
o VMS
o Apple Macintosh
o VM/CMS
o MVS
o MS DOS
Gopher was developed at the University of Minnesota.
Gopher User Image
A Gopher client offers an interface into "gopherspace", which appears
to the user as a hierarchy of menus and document nodes, similar in
some ways to a file system hierarchy of directories and files.
Selecting an entry from a menu node causes a further menu to appear,
or causes a document to be retrieved and displayed.
As well as "ordinary" document nodes, Gopher has "search nodes" when
one of these is selected from a menu, the user is prompted for one or
more words to search on. The result of the search is a "virtual"
menu, containing entries for document nodes (within some subset of
gopherspace) which match the search. A special type of Gopher search
server called "veronica" provides access to a database of all
directory nodes in gopherspace. This allows a user to construct a
virtual menu of all Gopher menu items containing a particular word.
WAIS databases may also be located at Gopher search nodes, since some
Gopher servers understand the format of WAIS index files.
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Gopher Protocol
Gopher uses a client-server paradigm. The Gopher protocol runs over
a reliable data stream service, typically TCP, and is fully defined
in RFC 1436. The following paragraphs give an overview which is
sufficient for understanding how multimedia data is handled in
Gopher.
A Gopher client opens a TCP connection to a Gopher server (defined by
machine name and TCP port number), and sends a line of text known as
the "selector" to request information from the server. The server
responds with a block of data, and then closes the connection. No
state is retained by the server. A null (empty) selector tells the
Gopher server to return its "root" menu node, containing pointers to
other information in gopherspace.
A menu is returned from a Gopher server as a sequence of lines of
text, each corresponding to one entry in the menu. Each line (which
is sometimes called a "Gopher reference") contains the following
data, which can be used by the client software to retrieve and
display the corresponding node in gopherspace.
o A single character which identifies the type of the node.
Possible values of this type ID are given below.
o A human-readable string which is used by the client software
when it displays the menu entry to the user.
o The selector which should be used by client software to
retrieve the node. It is treated as opaque by the client
software.
o The domain name of the host on which the node is held.
o The port number to use for the TCP connection.
A document node is sent by a Gopher server simply as lines of text
terminated by a dot on a line by itself, or as raw binary data, with
the end of the data indicated by the server closing the TCP
connection. The choice depends on the type of node.
The currently-defined type IDs are as follows:
0 Node is a file.
1 Node is a directory.
2 Node is a CSO phone book server.
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3 Error.
4 Node is a BinHexed Macintosh file.
5 Node is DOS binary archive of some sort.
6 Node is a UNIX uuencoded file.
7 Node is a search server.
8 Node points to a text-based telnet session.
9 Node is a binary file.
T Node points to a TN3270 connection.
Some experimental IDs are also in use:
s Node contains -law sound data.
g Node contains GIF data.
M Node contains MIME data.
h Node contains HTML data.
I Node contains image data of some kind.
i In-line text type.
The process for defining new data types and corresponding IDs is not
clear.
Gopher+ Protocol
The Gopher+ protocol is an extension of the Gopher protocol. Gopher+
is defined informally in [4]. It is designed to be downwards
compatible with the original protocol, so that old Gopher clients may
access Gopher+ servers (without being able to take advantage of the
new facilities), and Gopher+ clients may access old Gopher servers.
Gopher+ is still at the experimental stage, and is liable to change.
The most important new feature is the introduction of "attributes"
associated with individual nodes. The client may retrieve the
attributes of a node instead of the node contents. Attributes
defined so far include:
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INFO Contains the Gopher reference of the node.
Mandatory.
ADMIN Contains administrative information, including
the mail address of the server administrator and
the last-modified date of the node. Mandatory.
VIEWS Contains a list of one or more "view
descriptors", each of which describes an
alternate view of the node. For instance, an
image node may contain a TIFF view, a GIF view,
a JPEG view, etc. The client software (or the
user) may choose which view to retrieve. The
size of the view is also (optionally) available
in this attribute. The Gopher+ Attribute
Registry (see below) defines the permitted view
types.
ABSTRACT This attribute contains a short description of
the item. It may also include a Gopher
reference to a longer abstract, held in a
separate Gopher node.
ASK This attribute is used for the interactive query
extension. The interactive query facility in
Gopher+ is used to obtain information from a
user before retrieving the contents of a node.
The client fetches the ASK attribute, which
contains a list of questions for the user. His
or her responses to those questions are sent
along with the selector to the server, which
then returns the contents of the node. This
facility could be used as a very simple way of
querying a database, for instance. Using the
interactive query facility to supply a password
for access control purposes is not a good idea -
there are too many opportunities for
masquerading.
The University of Minnesota maintains a registry of Gopher+ attribute
types. For the VIEWS attribute, the registry contains a list of
permitted view types. Note that these view types have a similar
function to the type identifier described in the preceding section.
The general format of a Gopher+ view descriptor is:
xxx/yyy zzz: <nnnK>
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where xxx is a general type-of-information advisory, yyy is what
information format you need understand to interpret this information,
zzz is a language advisory (coded using POSIX definitions), and nnn
is the approximate size in bytes. Possible values for xxx include
text, file, image, audio, video, terminal.
(It now appears that the University of Minnesota Gopher Team accepts
the need to be consistent in the use of type/encoding attributes with
the MIME specification. The Gopher+ Type Registry may thus
eventually disappear, together with the set of xxx/yyy values it
currently contains.)
No view descriptors for directory nodes are currently registered.
In order to make use of the information available in attributes, it
is necessary to fetch the attributes before fetching the contents of
a node. Gopher+ provides a way of fetching the attributes for each
entry in a menu at the same time as the menu is retrieved. This
saves having to establish two successive TCP connections to fetch a
single document, at the expense of some additional client software
complexity.
Gopher Publishing
The procedure for making data available using the Unix Gopher server
"gopherd" is very straightforward. The hierarchical nature of the
Unix file system closely matches the Gopher concept of menus and
documents. The gopherd program exploits this - Unix directories are
represented as Gopher menu nodes, and Unix files as Gopher document
nodes. The names of directories and files are the entries in Gopher
menus. This can lead to awkward file names containing spaces, so
gopherd provides an aliasing mechanism (the \.cap directory) to get
round this.
To represent menu entries pointing to Gopher nodes on other servers,
special "link" files (starting with a dot) are used.
The type ID for a document node is determined from the extension of
its Unix filename. If a client requests a file containing a shell
script, the script is executed and the output returned to the client.
The Gopher+ version of gopherd is similar, but the .cap directory is
replaced by a configuration file gopherd.conf. This file is used to
specify administration attributes, and the mapping between filename
extensions and view descriptors. Some limited access control (based
on the client's IP address/domain name) is also provided by the
Gopher+ version of gopherd.
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Published Non-text Data
There is already some useful non-text data published on Gopher almost
exclusively image data. See for example the Vatican Library
Exhibition at the University of Virginia Library, the ArchiGopher at
the University of Michigan, the weather machine at the University of
Illinois. Some of these are described in the User Requirements
chapter of this report.
There seem to be rather fewer sound archives in gopherspace, but
interested users may access the Edinburgh University Computing
Service Gopher server on gopher.ed.ac.uk, where the Testing Area
contains 20 or 30 short audio files in Sun audio format. Note - the
availability of this archive is not guaranteed.
Advantages
The main factor in favour of Gopher is its widespread penetration.
There are over 1000 Gopher servers world-wide. This popularity is
due in part to the ease of setting up a Gopher server and making
information available on it, particularly on a Unix platform.
Limitations
It is unfortunate that the relatively well-defined MIME types were
not adopted in Gopher+. As mentioned above, this may yet happen,
although there appear to be reasons for keeping the set of MIME types
small whereas Gopher requires a wide range of types to offer to
clients. The latest word is that the MIME registry will be expanded
to include the types which the Gopher+ developers want.
Gopher is inflexibly hierarchical in nature. Hypertext or hypermedia
it is not - links to other nodes from within document nodes are not
possible. There is a suggestion in the Gopher+ specification that
alternate views of directory nodes could be used to provide some kind
of hypermedia capability, but this does not yet exist, and it is
unlikely that it could be made to work as easily as the WWW hypertext
model.
There is no access control at the user level - anyone can retrieve
anything on a Gopher server. There is no provision for charging for
information.
3.2. Wide Area Information Server
The Wide Area Information Server (WAIS) system allows users to search
for and retrieve information from databases anywhere on the Internet.
WAIS uses a client-server paradigm, and client and server software is
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available for a wide range of platforms. Client applications are
able to retrieve text or other media documents stored on the servers,
by specifying keywords. The server software searches a full-text
index of the documents, and returns a list of documents containing
the keywords (ranked according to a heuristic algorithm). The client
may then request the server to send a copy of any of the documents
found. Relevant documents can be fed back to a server to refine the
search. Successful searches can be automatically re-run, to alert
the user when new information becomes available.
WAIS was developed by Thinking Machines Corporation of Cambridge,
Massachusetts, in collaboration with Apple Computer Inc., Dow Jones
and company, and KPMG Peat Marwick. The WAIS software has been made
freely available; however Thinking Machines has announced that they
will stop support for their publicly-distributed WAIS as of version
8b5.1. Future support and development of the publicly-distributed
WAIS has been taken over by CNIDR (Clearinghouse for Networked
Information Discovery and Retrieval) in the USA. Future CNIDR
releases will be called FreeWAIS. A new company, WAIS Inc, has been
formed by Thinking Machines to take over commercial exploitation of
the Thinking Machines WAIS software.
WAIS server software is available for the following platforms:
o UNIX
o VAX/VMS
Client software is available for the following platforms:
o UNIX (versions for X, Motif, Open Look, Sun View)
o NeXT
o Macintosh
o MS DOS
o MS Windows
o VAX/VMS
There are currently over 400 WAIS databases available on the
Internet. WAIS is also the basis of some commercial information
services on private networks.
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WAIS User Image
In order to ask a question, the user must first select one or more
databases in which to look for the answer. (The list of all
available databases is available from a number of well-known sites.)
The next step is to enter one or more keywords as the basis of the
search. The search will return a list of documents (the "result
set") which contain any of the keywords. Each document is given a
ranking (a number between 1 and 1000) which indicates how relevant to
the user's question the server believes the document to be. The size
of each document is also shown in the list. The user may limit the
size of the result set - the default limit is typically 40 documents.
The user may then choose to retrieve and display one or more
documents from the list. Alternatively, he or she may designate one
or more documents in the list as "relevant", and perform another
search to find "more documents like this". This is called "relevance
feedback".
The user may retrieve general information about the database, and may
examine the catalogue of all documents in the database. There is
also a "database of databases", which may be searched to identify
WAIS databases which may be relevant to a subject.
WAIS Protocol
The user interface (client) talks to the server using an extended
version of a standard ANSI protocol called Z39.50. This is now
aligned with the ISO SR (Search and Retrieval) protocol for
bibliographic (library) applications, which is part of OSI. The
present WAIS protocol does not utilise a full OSI stack - APDUs are
transferred directly over a TCP/IP connection. The WAIS protocol is
described in [5].
WAIS does not, at this time, implement the full Z39.50-1992
specification - in particular, WAIS does not permit Boolean searches
(e.g., "find all documents containing 'chalk' and 'cheese' but not
'green'"). However, Boolean search capability is being added to the
FreeWAIS implementation. There are facilities in the Z39.50 protocol
for access control and charging, but these are not currently
implemented in WAIS.
The WAIS extensions to Z39.50 are mainly to provide the relevance
feedback capability.
Note that the Z39.50 protocol is not stateless - the result set may
in some circumstances be retained by the server for the user to
further refine or refer to. However, the subset of Z39.50 used by
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current WAIS implementations mean that server implementations may be
stateless.
Document type is determined by the server from information in the
database index (see below), and is sent to the client as part of the
result set.
WAIS Publishing
The first step in preparing data for publishing in a WAIS database is
to use the 'waisindex' utility. This takes a set of text files, and
produces an index file which contains an occurrence list of words of
three or more letters in every file. This index file is used by the
WAIS server software to resolve search requests from clients.
The 'waisindex' utility indexes files in a wide range of text
formats, as well as postscript and image files in various encodings
(only the file name is indexed for image files). Some of the text
formats involve a file as being treated as a collection of documents
for the purposes of WAIS access. Note that there appears to be no
formal "registry of types" - just whatever the waisindex program
supports. There is no distinction between media type and encoding
format.
Published Non-text Data
There is relatively little non-text data available in WAIS databases.
o URL=wais://quake.think.com:210/CM-images is a database of
TIFF images from the Connection Machine.
o URL=wais://mpcc3.rpms.ac.uk:210/home/images/pathology/RPMS-
pathology is a database of histo-pathological images and
documentation on mammalian endocrine tissue.
o URL=wais://starhawk.jpl.nasa.gov:210/pio contains GIF images
from NASA planetary probe missions, together with their
captions. The presence of the caption index information
makes it difficult to construct a search which returns
images in the result set increasing the maximum result set
size may help.
Advantages
WAIS is ideally suited for its intended purpose of searching
databases of textual information on the basis of keywords. It
appears to have the potential to satisfy the requirements of some of
the "database" category of applications mentioned in Chapter 1.
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Limitations
WAIS is not (and does not pretend to be) a general-purpose
information system, as Gopher and WWW are. WAIS does not have
hyperlinking, and offers a purely flat structure.
A limitation which is particularly apparent is the way that the
current version of FreeWAIS indexes non-text files - using only the
filename! However, it does seem that simply changing the indexing
program to allow a list of keywords to be attached to non-text files
would suffice to allow sensible indexing of non-text data. The
commercial (WAIS Inc) version of WAIS allows several files to be
associated together for indexing and retrieval purposes.
Furthermode, the UCSF Centre for Knowlege Management is modifying the
FreeWAIS code to support the indexing of multiple content types. The
document returned by WAIS will be an HTML document containing
pointers to the multimedia data. Contact dcmartin@library.ucsf.edu
for further information.
WAIS is not a fully-featured query/response protocol such as SQL. It
has no concept of fields, or numeric data types.
It appears to be impossible to retrieve a document from its catalogue
entry in many of the existing databases.
3.3. World-Wide Web
The World-Wide Web project (also known as WWW or W3), started and
driven by CERN, is a large-scale distributed hypertext system. It
uses the standard client-server paradigm, with client "browser"
software responsible for fetching and displaying data. Originally
aimed at the High Energy Physics community, it has spread to other
areas.
Browser software is available for a large number of systems
including:
o Line-mode dumb terminal.
o Terminal with Curses support
o Macintosh
o X/Motif
o X11
o PC/MS Windows
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o NeXT
There is server software available for:
o VM mainframes.
o UNIX
o Macintosh
o VMS
WWW User Image
The WWW world consists of nodes (usually called documents) and links.
Links are connections between documents: to follow a link, a reader
clicks with a mouse on a word in the source document, which causes
the linked-to document to be retrieved and displayed. (On systems
without a mouse, the user types a number instead.)
Indexes are special documents which, rather than being read, may be
searched. To search an index, a reader supplies keywords (or other
search criteria). The result of a search is a "virtual" document
containing links to the documents found. All documents, whether
real, virtual or indexes, look similar to the reader.
The WWW addressing mechanism means that an interface to Gopher and
anonymous FTP information sources may be established, in a way which
is transparent to the user. Thus, the whole of gopherspace is part
of the Web. Transparent gateways to other systems, including Hyper-G
and WAIS, are also available.
URL
All nodes on the Web are addressed using the "Universal [or Uniform]
Resource Locator" (URL) syntax, defined in [6]. This is an Internet
Draft produced by the IETF URL Working Group.
A URL is a name for an object (which may be a document or an index)
on the Internet. It has the general form:
<scheme> : <path> [ # <anchorid> ]
The <scheme> identifies an access protocol or method for the object.
Some of the schemes are HTTP (the native WWW protocol), anonymous
FTP, Andrew file system, news, WAIS, Gopher. The <path> component
locates the document in a way significant for the access method.
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Thus for instance for anonymous FTP, the path includes the fully
qualified domain name of the host on which the document resides, and
the directory and file name under which it may be found. For some
schemes, the <path> may include a search string (or combination of
strings) which is used to address a "virtual" object formed by
searching an index of some kind. The HTTP, WAIS and Gopher schemes
can use search strings, which usually follow the rest of the path,
separated from it by a ?.
The optional <anchorid> is used for addressing within an object. Its
interpretation is not defined in the URL specification.
"Partial" URLs may be specified. These are used within a document on
the Web to refer to another "nearby" document - for instance to a
document in another file on the same machine. Certain parts of the
URL (e.g., the scheme and machine name) may be omitted, according to
well-defined rules. This makes it much easier to move groups of
documents around, while maintaining the links within and between
them.
A URL locates one and only one object on the Internet. However, more
than one URL may point to the same object. Given two URLs, it is not
in general possible to determine whether they refer to the same
object. Furthermore, there is no guarantee that a single URL will
refer to the same object at different times (the object may change
incrementally, or it may be completely replaced with something
different, or it may indeed be removed).
HTTP
HTTP (HyperText Transfer Protocol) is the protocol employed between
server and client. It is defined in [7]. The protocol is currently
being revised (see the Future Developments section below), and will
eventually be proposed as an Internet standard.
The original protocol is extremely simple, and requires only a
reliable connection-oriented transport service, typically TCP/IP.
The client establishes a connection with the server, and sends a
request containing the word GET, a space, and the partial URL of the
node to be retrieved, terminated by CR LF. The server responds with
the node contents, comprising a text document in the Hypertext Markup
Language (HTML). The end of the contents is indicated by the server
closing the connection.
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HTML
HTML (HyperText Markup Language) is the way in which text documents
must be structured if they are to contain links to other documents.
Non-HTML text documents may of course be made available on the Web,
but they may not contain links to other documents (i.e., they are
leaf nodes), and they will be displayed by browsers without
formatting, probably using a fixed-width font. Like HTTP, HTML is
also undergoing enhancement, but the original version is defined in
[7], and is being submitted as an Internet draft.
HTML is an application of SGML (Standard Generalized Markup
Language). It defines a range of useful tags for indicating a node
title, paragraph boundaries, headings of several different levels,
highlighting, lists, etc. Anchors are represented using an <A> tag.
For instance, here is an example of HTML containing an anchor:
The HTTP protocol implements the WWW <A NAME=13
HREF="../../Administration/DataModel.html">data model</A> .
The location of the anchor is the text "data model". It is a source
anchor, with a target given by the URL in the HREF attribute, so the
text would appear highlighted in some way in a client's window, to
indicate that clicking on it would cause a hyperlink to be traversed.
It is also a target anchor, with an anchor ID given by the NAME
attribute. A source anchor referring to this target would specify
#13 at the end of the node's URL. Traversing a hyperlink to this
node would cause the entire node to be retrieved, but the target
anchor text would be displayed in some emphasised way - for instance
if the retrieved text is displayed in a scrolling window, it might be
positioned such that the target anchor appears at the top of the
window.
Another attribute of the <A> element, TYPE, is also available, which
is intended to describe the nature of the relationship modelled by
the link. However, this is not in extensive use, and there appears
to be no registry of the possible values of such types.
Future Developments
HTTP and HTML are currently being extended in a backward-compatible
way to add multimedia facilities. [8] describes the HTTP2 protocol.
The revised HTML is defined in [9]. Both documents are subject to
change (and indeed the HTML2 specification has changed substantially
during the preparation of this report).
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The revised HTML contains many enhancements which are useful for
multimedia support. Some of the most relevant are listed below.
o "Universal Resource Numbers" are a proposed system for
unique, timeless identifiers of network-accessible files
presently being designed by IETF Working Groups. URNs must
be distinguished from URLs, which contain information
sufficient to locate the document. URNs may be allocated to
nodes and may be represented in source anchors. This saves
client software from retrieving a copy of something it
already has - allowing sensible caching of large video
clips, for instance. The disadvantage is that when
something is changed and given a new URN, the source anchors
of all links which point to it must be changed (and the URNs
of these documents must therefore be changed, and so on).
Therefore, it makes sense to allocate URNs only to very
large documents which change rarely, and not to the
documents which reference them.
o The title of a destination document may be included as
anattribute of a source anchor. This allows a client to
display the title to the user before or during retrieval,
and also allows data which does not itself contain a title
(e.g., image data) to be given one.
o There is provision for in-line non-text data (e.g., images,
video, graphics, mathematical equations), which appears in
the samewindow as the main textual material in the node.
o The concept of the relationship expressed by a hyperlink is
expanded. Both source and target anchors may contain
relation attributes which point forwards and backwards
respectively. Possible relationships include "is an index
for", "is a glossary for", "annotates", "is a reply to", "is
embedded in", "is presented with". The last two are useful
for multimedia - for instance, the "embed" relationship
could cause a retrieved image to be fetched and embedded in
the display of a text node, and the "present" relationship
could cause a sound clip to be automatically retrieved and
presented along with a text node.
The HTTP2 protocol maintains the same stateless
connect/request/response/close procedure as the current HTTP
protocol. Data is transferred in MIME-shaped messages, allowing all
MIME data formats (including HTML) to be used. As well as the GET
operation, HTTP2 has operations such as:
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HEAD Fetch attribute information about a node
(including the media type and encoding)
CHECKOUT/CHECKIN/PUT/POST
These allow nodes to be checked out for updating
and checked back in again, and new nodes to be
created. New node data is supplied in MIME
shape with the request.
The request from the client can contain a list of formats which the
client is prepared to accept, user identification, authorisation
information (a placeholder at present), an account name to charge any
costs to, and identification of the source anchor of the hyperlink
through which the node was accessed.
The response from the server may contain a range of useful attributes
(e.g., date, cost, length - but only for non-text data). The server
may redirect the query, indicating a new URL to use instead. It may
also refuse the request because of authorisation failure or absence
of a charge account in the request.
The protocol also contains a mechanism which is designed to allow the
server to make an intelligent decision about the most appropriate
format in which to return data, based on information supplied in the
request by the client. This may for instance allow a powerful server
to store the uncompressed bitmap of an image, but to compress it on
request using an appropriate encoding, according to the decoding
capabilities announced by the client.
An HTTP2 server and client are currently under test. Some HTML2
features are already fitted to the XMosaic browser.
Mosaic
The Mosaic project, located at the US National Centre for
Supercomputing Applications (NCSA) at the University of Illinois, is
developing a networked information system intended for wide-area
distributed asynchronous collaboration and hypermedia-based
information discovery and retrieval. Mosaic, which is specifically
oriented towards scientific research workers, has adopted the World
Wide Web as the core of the system, and the first Mosaic software to
appear was the XMosaic WWW client for UNIX with X. Other clients of
similar functionality are under development for the Apple Macintosh
and the PC with Windows.
The capabilities of the XMosaic browser include:
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o Support for NCSA's Data Management Facility (DMF) for
scientific data.
o Support for transferring data with other NCSA tools such
asCollage, using NCSA's Data Transfer Mechanism (DTM).
o The ability to "check out" documents for revision, and to
check them back in again.
o Local and remote annotation of Web documents.
Future planned functionality includes:
o In-line non-text data (in addition to images).
o Information space graphical representation and control.
o Hypermedia document editing.
o Information filtering.
NCSA intends to make the entire Mosaic system publicly available and
distributable.
The XMosaic browser was used extensively for finding and retrieving
information used to prepare this report.
Web Publishing
Making a web is as simple as writing a few SGML files which point to
your existing data. Making it public involves running the FTP or HTTP
daemon, and making at least one link into your web from another. In
fact, any file available by anonymous FTP can be immediately linked
into a web. The very small start-up effort is designed to allow small
contributions.
At the other end of the scale, large information providers may
provide an HTTP server with full text or keyword indexing. This may
allow access to a large existing database without changing the way
that database is managed. Such gateways have already been made into
Digital's VMS/Help, Technical University of Graz's "Hyper-G", and
Thinking Machine's WAIS systems.
There are a few editors which understand HTML - for instance on UNIX
and on the NeXT platform.
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Published non-text data
See the multimedia demo node on:
http://hoohoo.ncsa.uiuc.edu:80/mosaic-docs/multimedia.html
This contains links to images, sound, movies and postscript media
types. The media type is determined by the filename extension in the
URL specification of the target node. The (XMosaic) client uses this
to invoke a separate program appropriate for displaying the media
type, or in some cases it can be displayed embedded within the source
document. The latter method uses an <IMG> tag, which is part of
HTML2.
Advantages
WWW is a hypertext system and its underlying technology is thus
richer than Gopher. The use of SGML, which is of increasing
importance in hypermedia systems, allows a great deal of
expressiveness and structure, and enables text to be presented in an
attractive way. The facilities for multimedia data in the extended
versions of HTTP and HTML are excellent. It also seems that QOS and
management issues identified in Chapter 2 are to some degree catered
for in these extensions.
Limitations
There is no indication in the source anchor of the media type of the
destination node, or of its size (this has been ruled out on the
argument that the information is likely to degrade with time). It is
necessary to perform a HEAD request (in HTTP2) to deduce this.
Link source anchors must be in text documents, so non-text nodes must
be leaf nodes. However, with HTML2 using the <IMG> tag, an embedded
bitmap may be used as a source anchor, and the position of the mouse
click within the image is passed to the server, which can then choose
to return a different document depending on where in the image the
mouse was clicked.
WWW is much less prevalent than Gopher, partly because of an
(erroneous?) perception that setting up an HTTP server is more
complex than setting up a Gopher server. There are only about 60
servers world-wide; however the growth in the use of WWW is much
faster than the growth in the use of Gopher. The availability of
sophisticated WWW clients such as XMosaic is fuelling this growth.
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3.4. Evaluating Existing Tools
This section compares the capabilities of the Gopher, WAIS and
WorldWide Web systems (abbreviated as GWW) to the informal
requirements defined in section 2.3.
Platforms
The table below gives the names of the most important client software
for each of GWW on the three most important platforms of interest.
WWW is the weakest, with clients for the Macintosh and the PC still
under development. The main PC Gopher client is "PC Gopher III",
which is a DOS program, not a Windows program.
CLIENTS Gopher WAIS WWW
Macintosh TurboGopher WAIStation (No name)
(beta version
available)
PC with HGopher (two WAIS for Cello (beta
Windows others also Windows, WAIS version
available) Manager available),
Mosaic (beta due
3Q93)
UNIX with X Xgopher, XWAIS XMosaic
XMosaic
At present, multimedia support in most of these clients (where it
exists) is limited to the invocation of external "viewer" programs
for particular media types. The exception is XMosaic, which supports
in-line images in WWW documents.
Media Types
The GWW tools can all handle multiple media types well.
o Text is very well supported by all three tools. WWW offers
facilities for displaying "richer" text, supporting
headings, lists, emphasised text etc., in a standardised way.
o Image data is also well supported, using either external
viewers (e.g., the TurboGopher client software on a Macintosh
might invoke the JPEGView program to display an image); or
in-line display within a text document (WWW with XMosaic on
UNIX).
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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.
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Gopher menus can be constructed to allow alternative views of
gopherspace. For instance, a geographically-organised menu tree of
gopherspace is in place, but a parallel subject-based menu tree could
be added as an alternative way of access to the same data. (There
are in fact moves to set this up.) Since WWW offers a superset of
Gopher functionality, these comments also apply to the Web. In fact,
the Web already has a rudimentary subject tree.
In both Gopher and WWW, non-textual data may be used in different
information structures without having to maintain more than one copy.
Presentation
There is little support in GWW for controlling the presentation of
non-text data.
o Backdrops are not supported by GWW.
o Buttons are supported in a limited way - typically, a node
is retrieved by clicking on a highlighted text phrase, or on
an entry in a list. In XMosaic, bitmap images can be used
as buttons. However, there is no support for different
styles of button. Client software may have generic
navigation buttons (e.g., "Back", "Next", "Home") which are
always available and don't form part of a node.
o Synchronisation in space is not supported by GWW, except
that WWW supports contextual synchronisation of images using
the <IMG> tag.
o Synchronisation in time is not supported by GWW.
Searching
WAIS supports keyword searching, and is very well suited for that
task. The Gopher+ protocol could potentially support multimedia
database querying applications through the ASK attribute, but there
is as yet no server implementation which supports such database
applications. In the WWW project, there are ongoing discussions on
how best to extend HTML to cope with database query applications - an
<INPUT> tag has been suggested - but no consensus has yet emerged.
Both Gopher and WWW can make use of WAIS-type keyword searching:
either by incorporating WAIS code into the server (enabling WAIS
index files to be searched); or through WAIS gateways, which run
searches on remote WAIS servers in response to queries from non-WAIS
clients.
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Interaction
XMosaic allows users to make text (or on some platforms, audio)
annotations to any text node. The annotations appear at the end of
the text display.. They are held locally - other users of the node
do not see the annotations (but a recently added facility allows
globally-visible annotations held on an "annotation server"). Text
annotations may include hyperlinks to other nodes (provided the user
knows how to use HTML). Other clients do not provide such
facilities.
There is a move to add an "email" address notation to URL. This
would allow WWW client software to invoke a mail program when a user
selects an anchor with such a URL.
There are plans to allow WWW users to delineate a rectangular area of
interest within an image for use in an HTTP request.
There is no support in GWW clients for interacting with sequences of
images in the way described in section 2.3.6.
Quality of Service
The user expectations for responsiveness mentioned in section 2.3.7
are difficult to meet with currently-deployed wide-area network (or
even LAN) technology, particularly for voluminous multimedia data.
None of the GWW systems currently exploit the emerging isochronous
data transfer capabilities of protocols such as RTP and technologies
such as ATM. None of them make serious attempts to alleviate the
problem in other ways (except for WWW, which defines some mechanisms
in HTTP2 for format negotiation based on size and available bandwidth
considerations).
Management
The following table shows the support for three key management
facilities in the GWW systems. The first two facilities require
support in the client/server protocol, the third requires support in
the server, but depends on authentication being available.
Gopher WAIS WWW
Access control No No1 Yes, in
and HTTP2
authentication
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Charging support No No Yes, in
HTTP2
Monitoring for No No No
statistical and
assessment
purposes
Note:
1. "Access-control-facility" is a feature of Z39.50 which is not used
by the current WAIS implementations.
Scripting Requirements
None of the GWW systems have facilities for the execution of scripts
by the client, because of security issues (it would be too easy for a
malicious "trojan" script to be executed). Gopher and WWW servers
have the ability for a UNIX script to be run by the server, with the
script output returned to the client. Scripting as understood in the
context of stand-alone multimedia applications does not exist in GWW.
Bytestream Format
None of the three GWW systems use a bytestream format for
interchanging collections of material. There has been some talk
about setting up a system akin to the "Trickle" mail server, for
retrieving single document nodes from GWW using mail. Such a system
has been implemented for WWW.
Authoring tools
Gopher is sufficiently simple to set up that no special authoring
tools are required. WAIS requires only an indexing program (as
discussed in section 3.2) for preparing material for publication.
WWW, because it uses a sophisticated authoring language (HTML),
benefits from the availability of authoring tools. There are HTML
editors for UNIX (using the tk toolkit) and the NeXT system. There
are no authoring tools designed specifically for exploiting the
multimedia capabilities of WWW, mainly because these capabilities are
still evolving.
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4. Research
This section describes some current research projects in the area of
distributed hypermedia information systems.
4.1. Hyper-G
Hyper-G [10] is an ambitious distributed hypermedia research project
at a number of institutes of the IIG (Institutes for Information-
Processing Graz), the Computing and Information Services Centre of
the Graz University of Technology, and the Austrian Computer Society.
It is funded by the Austrian Ministry of Science. It combines
concepts of hypermedia, information retrieval systems and
documentation systems with aspects of communication and
collaboration, and computer-supported teaching and learning.
Unlike WWW, Hyper-G supports bi-directional links. This enables
users to see which other documents reference the one they are using,
and also allows the system to avoid dangling pointers when a linkedto
document is deleted. Another difference from WWW is that links are
kept separately from their source and target nodes, to allow easy
linking of read-only documents and for ease of link maintenance. In
addition to manually defined links, Hyper-G supports automatic static
and dynamic (i.e., view-time) generation and maintenance of links.
Hyper-G has a concept of generic "structures" - an additional layer
of relationships imposed on (and orthogonal to) the web of documents
and links. A document can be part of more than one structure, and
structures may be hierarchically related. Types of structure
include:
o "Clusters" are a set of documents which are all
presentedtogether.
o "Collections" are unordered sets of documents or other
structures, and can be used as query domains or to construct
gopher-like menus.
o "Paths" are ordered sets of documents or structures, which
must be visited sequentially.
One application of the structure concept is the provision of "guided
tours" through the information space.
In addition to hypernavigation, the collection hierarchy and guided
tours, another strategy for interaction with the system is the use of
database queries. Two kinds of query are supported: keyword
searching in a user-defined list of databases; and collection
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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).
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There are suggestions that this standard could be used as a query
language in conjunction with the HyQ query component of the HyTime
standard.
DFR
DFR is the Document Filing and Retrieval system, specified in ISO
10166-1 and ISO 10166-2. It is intended for office automation
applications, and falls within the Distributed Office Applications
(DOA) model of ISO 10031-1. DFR has design similarities to the ISO
Directory and to the X.400 Message Store, and it is likewise part of
OSI.
DFR defines a Document Store, which provides a service to a DFR User
over an OSI protocol stack incorporating ROSE (and optionally RTSE).
A document in the Document Store may have a number of attributes
associated with it, including pointers to related documents. There
is support for multiple versions of the same document, and for
hierarchical groups of documents. The access protocol supports
searching for documents based on their attributes. DFR itself does
not restrict the content of documents in any way, but the natural
partner to DFR is the ODA standard for document content.
It is not clear that DFR offers significantly more useful
functionality than is available from other, simpler access protocols
already in use on the Internet.
5.3. Other Standards
This section briefly describes other standards in this area and
discusses their relevance.
MIME
MIME (Multipurpose Internet Mail Extensions) is a mechanism for
transferring multimedia information in an RFC822 mail message. STD
11, RFC 822 defines a message representation protocol which specifies
considerable detail about message headers, but which leaves the
message content as flat ASCII text. RFC 1341 redefines the format of
message bodies to allow multi-part textual and non-textual message
bodies to be represented and exchanged without loss of information.
Because RFC 822 said very little about message content, RFC 1341 is
largely orthogonal to (rather than a revision of) RFC 822.
MIME provides facilities to include multiple objects in a single
message, to represent text in character sets other than US-ASCII, to
represent formatted multi-font text messages, to represent non
textual material such as images and audio fragments, and generally to
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facilitate later extensions defining new types of Internet mail for
use by co-operating mail agents. It does not define any structure to
allow relationships between body parts within a message to be
expressed.
For the purposes of the requirements considered by this report, the
relevance of MIME is that it separates media type from media
encoding, and that it defines a procedure for registering values of
these attributes.
The MIME construct of chief interest is the "Content-Type" field.
This contains a MIME "type" and "subtype", and any "parameters" which
further qualify the subtype. The register of MIME content-types is
maintained by the Internet Assigned Numbers Authority (IANA). Content
types defined in the MIME standard itself include:
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Type Subtype Parameters Meaning
text plain charset Plain text
richtext charset Text with SGML-like
markup for
representing
formatting.
image jpeg JPEG File Interchange
Format
gif Graphics Interchange
Format
audio basic 8-bit -law 8kHz PCM
encoding
video mpeg
application ODA profile Open Document
(used (Document Architecture
for Application document.
application Profile)
-specific
data)
octet- name (e.g., General binary data
stream filename); such as an arbitrary
type (for binary file.
human
recipient),
etc.
postscript Document in
postscript.
Private experimental values of types and subtypes starting with X may
be used between consenting adults without registration with IANA.
MIME also defines a "Content-Transfer-Encoding" field, which is used
to specify an invertible mapping between the "native" encoding of a
media type and a representation that may be readily exchanged using
7bit mail transfer protocols.
WWW's HTTP2 protocol makes use of MIME media type and encoding
attributes, and also uses MIME's message format for retrieving data
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from the server. It is the first MIME application to utilise the
8bit Content-Transfer-Encoding, which essentially means no encoding.
SMSL
SMSL is the Standard Multimedia Scripting Language. It is a proposed
new work item for ISO/IEC JTC1/SC18/WG8 (HyTime) and JTC1/SC29/WG12
(MHEG). The functional requirements are expected to be completed in
1994, and the coding scheme completed in 1995.
SMSL is designed as an open language with a similar purpose to
existing vendor-specific scripting languages such as Macromind's
"Lingo", Kaleida's "Script/X", and Gain's "GEL". The intention is to
offer an intermediate open multimedia scripting language which could
be used both for interchange purposes, and for controlling the
presentation of HyTime or MHEG multimedia structures. Several
different approaches to defining SMSL have been suggested, including
using the ANDF (Architecture-Neutral Distribution Format) approach,
and basing SMSL on SGML or on the Scheme language.
The SMSL work is not sufficiently advanced to permit a judgement of
its usefulness in satisfying the requirements under discussion.
However, it is interesting to note that despite the descriptive power
of HyTime and MHEG, there is still perceived to be a role for
procedural scripting.
AVIs
The CCITT is defining a set of Audio Visual Interactive Services
(AVIs), intended for offering to domestic and business consumers over
a national network (e.g., by PTTs). These services will be specified
as T.17x recommendations, and will include MHEG. These services
would also make use of the SMSL work.
Insufficient information is available about this area to allow its
relevance to be judged.
5.4. Trade Associations
This section mentions some trade associations which are involved in
standards making in the multimedia area.
Interactive Multimedia Association
The Interactive Multimedia Association (IMA) is an international
trade association with over 250 members, representing a wide spectrum
of multimedia industry players. Members include Apple, Microsoft,
MIT CECI (the developers of AthenaMuse 2), 3DO, and many other
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important market actors.
In 1989, the IMA initiated a "Compatibility Project", tasked with
developing technical solutions to the cross-platform compatibility
problem. The Project has published two important documents:
o "Recommended Practices for Multimedia Portability" [23]
outlines a specification for a common interface to be used
by interactive video delivery systems. It has been adopted
by the US Military as part of Military Standard 1379.
o "Recommended Practices for Enhancing Digital Audio
Compatibility in Multimedia Systems" [24] defines four
standard digital audio data types and four sampling rates
(from low-end -law 8kHz mono encoding, up through ADPCM
modes to CD-quality 44kHz 16-bit stereo).
Work is continuing to produce further recommendations on other
issues.
The Compatibility Project has now initiated a procurement process by
publishing three Request for Technology (RFT) documents, defining the
requirements of a platform-independent interactive multimedia system,
including networking requirements. The RFTs cover "Multimedia System
Services", a "Scripting Language for Interactive Multimedia Titles",
and "Multimedia Data Exchange". An "Architecture Reference Model"
for cross-platform desktop and distributed multimedia systems
provides the framework for these RFTs, which are pragmatic documents
outlining the technical requirements for time-based media handling in
detail. Note that relatively little is said about non-time-based
data.
A first reading of the Multimedia Data Exchange RFT reveals that the
Apple Bento standard [18] and the Microsoft/IBM RIFF format [25] both
influenced the development of this document. The selected system may
well be based on one or both of these technologies.
A joint response to the Multimedia System Services RFT has been
received from HP, IBM and Sun. Two responses to the Scripting
Languages RFT have been received - from Kaleida (Script-X) and Gain
Technology (GEL). Two partial responses to the Multimedia Data
Exchange RFT have been received from Apple (Bento) and Avid (Open
Media Framework).
Responses to the RFTs are currently being analysed by the IMA, and
the result will be announced in November 1993. The specifications
which will eventually result from this process will be important for
future commercial multimedia products. It is important that the
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community keep a watching brief on the IMA Compatibility Project and
its possible implications for distributed multimedia applications on
the Internet.
Multimedia Communications Forum
The Multi-Media [sic] Communications Forum (MMCF) is a recently
formed (June 1993) trade consortium whose initial members include
IBM, National Semiconductor, Apple, Siemens and AT&T. Intended to
complement the work of the IMA, the MMCF plans to develop guidelines
and recommendations for the industry to help ensure "end-to-end
network interconnectivity of multimedia applications, workstations
and devices". They also plan to provide input to standards bodies.
It is still too early to say whether this forum will succeed. If the
IMA Compatibility Project specifications, when they are published,
leave networking issues open, then MMCF could have an important role
to play. It is recommended that RARE consider becoming an Observing
Member ($350 US pa), entitling it to attend general and annual MMCF
meetings (but not committee meetings), and to receive minutes and
other general papers (but not working documents); with the prospect
of becoming an Auditing Member ($1200 US pa) later if relevant.
Multimedia Communications Community of Interest
This is a very new organisation formed at a meeting in France in June
1993. Its charter is to promote the use of applications which let
people in different locations view documents, images, graphics and
full-motion video on a PC screen. The remit includes CSCW aspects.
Members of the organisation include IBM, Intel, Northern Telecom,
Telstra (Australia), BT, France Telecom and DB Telekom. The
companies plan field trials of multimedia services in 1Q94.
6. Future Directions
6.1. General Comments on the State-of-the-Art
Distributed hypermedia systems are now emerging from the research
phase into the experimental deployment stage. Every project team
(and standards committee), almost without exception, hopes for their
system to become the de facto standard for hypermedia.
As we've seen, Gopher and WWW already offer multimedia capability,
but they are still largely oriented to the use of external viewers
for non-text nodes. This "unintegrated" approach is in contrast to
typical stand-alone multimedia applications, where the presentation
of related information in different media is tightly integrated. The
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in-line image feature of XMosaic and the new version of HTML
currently under development may represent the start of a move towards
greater integration of different media in such distributed hypermedia
systems.
Three important factors in the design of distributed hypermedia
systems appear to emerge from the preceding chapters of this report.
They can each be formulated in terms of distinctions between two
aspects of the system.
o A common and apparently fruitful approach to hypermedia
systems is to distinguish the content from the
hyperstructure. Standards work clearly distinguishes
between these concepts, with standards such as MPEG, JPEG,
G.72x, etc, for content; and HyTime or MHEG for structure.
Currently-deployed systems also make this distinction, most
obviously in Gopher, where the structure/content split maps
onto the server filesystem's directory/file split. In a
similar way, the ability to maintain hyperlink information
separately from data is perceived in hypermedia research
circles as a "good thing". Research systems such as
Microcosm and Hyper-G do this, and HyTime with its ilink
element also supports it. WWW does not support this, but
requires link anchors to be edited into source data. There
are problems with this approach, however - see the section
on Microcosm for details.
o A useful approach to content is to distinguish the media
type from the media encoding. The MIME standard (used by
HTTP2) illustrates how this can be done, and Gopher+ employs
a similar system.
o The distinction between data and protocol is also important
for some systems. WWW for instance has clearly separate
protocol (HTTP) and data (HTML) specifications. However,
Gopher+ is specified without making this distinction. (The
original Gopher system is very simple and arguably has no
need for such separation.)
The most significant mismatches between the capabilities of
currentlydeployed systems and user requirements are in the areas of
presentation and quality of service. Adding flexibility in
presentation capabilities to WWW or Gopher should be possible without
any major change to the protocols (although it may require changes to
data formats). Such capabilities could result from the progress
towards greater integration of media types presaged above. However,
improving QOS is significantly more difficult, as it may require
changes at a more fundamental level. The following section outlines
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some possible solutions to this problem.
6.2. Quality of Service
Meeting the responsiveness requirement is certainly the key factor
for the acceptance of networked multimedia information systems in the
user community. To reiterate the requirement given in a previous
section:
o For simple actions such as "next page", tolerable delays are
of the order of 0.2s.
o For more complex actions such as "search for documents
containing this word", then a tolerable delay is of the
order of 2s.
o Users tend to give up waiting for a response after about
20s.
There are several methods which may alleviate the problem of poor
responsiveness (or cause the user to revise his or her expectations
of responsiveness!), some of which are described below.
1. Give clues that fetching a particular item might be time-
consuming - simply quoting the size (and/or location) may be
sufficient. WAIS and some Gopher clients already quote the
size.
2. Display a "progress" indicator while fetching data.
3. Allow the user to interact with other, previously fetched
information while waiting for data to be retrieved. The
inability to do this is an annoying limitation of XMosaic.
It can be difficult to implement, except on a multi-threaded
operating system such as OS/2 or Windows NT.
4. Allow several fetches to be performed in parallel. Again,
multithreading support makes this easier. This technique is
less likely to be useful if all the nodes being requested
come from the same server.
5. Pre-fetch information which the client software believes the
user will wish to see next. This requires some "hints" in
the data about which nodes might be good candidates for pre-
fetching.
6. Cache information locally. The use of Universal Resource
Numbers (see the section on WWW) is relevant for managing
this.
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7. Where multiple copies of the same information are held in
different network locations, fetch the "nearest" copy. This
is sometimes known as "anycasting", and is a more general
case of local caching. The proposed URN-to-URL resolution
service [26] could be used to support this.
8. When retrieving a document, the client should be able to
display the first part of the document to the user. The
user can then start to read the document while the system is
still downloading it. Alternatively, the user may decide
that the document is not relevant and abort the retrieval.
9. Offer multiple views of image or video data at different
resolutions and therefore sizes. This enables the user to
select a balance between speed of retrieval and data
quality. Gopher+ and HTML2 both support this.
10. Future high-speed networks and protocols (ATM, RTP) will
allow real-time display of isochronous data. Information
systems should be able to take advantage of this.
A useful description of the problem is given in [27]. This paper
rightly contends that the view, held by many hypermedia researchers
and implementors, that the network is simply a transparent data
highway which needs no special consideration in application design,
is wrong. It is argued that:
"the very same structural characteristics that may make
a multimedia document appealing to the end user are the
characteristics that are extremely helpful during
dynamic network performance optimisation".
This is a particularly relevant statement considered in the light of
suggestion 5 above.
6.3. Recommended Further Work
To meet the needs of applications such as those described in section
2.1, the community must seek where possible to adapt and enhance
existing tools, not to build new ones. There is now an opportunity
for RARE to stimulate and encourage this process of adaptation and
enhancement, and the following subsections outline a strategy for
this.
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Selecting a System
In order to have the greatest effect, RARE should concentrate its
efforts on only one of the existing tools. Candidate technologies
are those already outlined: Gopher, WWW, WAIS, Hyper-G, Microcosm and
AthenaMuse 2.
It is recommended that RARE should select the World-Wide Web to
concentrate its efforts on. The reasons for this decision are as
follows.
o Flexibility. The rich yet straightforward design of WWW,
with its clearly separable components (HTML, URL and HTTP),
means that it is a very flexible basis on which to develop
distributed multimedia applications.
o Existing efforts. The WWW implementor community is already
discussing and designing extensions to HTML (HTML2),
intended (among other things) to support multimedia. There
is clearly much interest in this area, and RARE efforts
could complement existing work.
o Hyperlinks. A clear requirement of many applications is the
availability of hyperlinking, which WWW supports well.
o Integrated solution. Because WAIS, Gopher and Hyper-G (as
well as anonymous FTP servers) may all be accessed from Web
clients, WWW serves as an important integrating tool for
information services. It is important that distributed
multimedia applications, which require extensive support in
the client software, should be based on a technology "close
to" such integrated clients.
o Penetration and growth. Although Gopher far surpasses WWW
in the number of servers available, the rate of growth in
WWW usage is greater than that of Gopher. There is an
increasing realisation in the community that Gopher is over-
simplistic for many purposes, and a corresponding increase
in interest in WWW.
o Attention to QOS issues. There is already an awareness in
the WWW community of the need for achieving an appropriate
QOS, and a mechanism has already been proposed in HTTP2 to
alleviate the problem.
o Standardisation. The WWW team is taking standardisation of
the existing WWW system components seriously. The URL
format has already been published as an Internet draft (and
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has been adopted as an important component of the proposed
Internet integrated information infrastructure), and the
current version of HTML is about to follow suit. The use of
SGML as the basis of HTML complies with the perceived
importance of SGML for hypermedia in general (and also fits
in with RARE's approach of adopting appropriate open
standards).
o Software status. CERN has recently placed the WWW code
developed by it into the public domain. This is unlike all
the other candidate technologies, which all have
restrictions on who can do what with the code. In the case
of Gopher, these restrictions are already causing some
commercial users to look at other options.
WWW has two significant disadvantages, both of which are being
alleviated:
o Restricted choice of client software. At present, Apple
Macintosh and PC/MS Windows clients are available in beta
form only. By contrast, there are more than one well-tested
Gopher clients available for these platforms.
However, other WWW clients for the Mac and MS Windows are in
the pipeline.
o There is a perception in the community that making
information available over HTTP is difficult, and that it
must be put into HTML.
However, it is possible to put plain-text, non-HTML
documents onto the Web. Such documents of course cannot
contain links.
Furthermore, WYSIWYG HTML text editors are available, to
ease the pain of writing HTML.
The main disadvantages of the other systems are:
o Gopher is designed for simplicity, and therefore lacks the
flexibility of WWW. In particular its structure is too
inflexibly hierarchical and it does not have hyperlinks.
Its main advantage is its very heavy penetration. However,
because of the WWW approach to accessing data using other
protocols, all of gopherspace is part of the Web. Any Web
client should be able to be a gopher client too.
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It is neither envisaged that Gopher will go away, nor that
it won't be used for multimedia data. However, Gopher is
unlikely to be used for more sophisticated multimedia
applications such as academic publishing, interactive
multimedia databases and CAL, because of the above-mentioned
limitations.
o WAIS is a specialised tool, and will certainly form part of
the overall solution, particularly for database-type
applications. It is not a general solution for distributed
hypermedia applications.
o AthenaMuse 2 is commercially-oriented: it is clear that
academic and research users will have to pay to use the
software. Its level of use is thus very unlikely to be as
great as publiclyavailable systems such as WWW. Moreover,
it does not support all the required platforms.
o Microcosm network support is still in early stages, limited
at present to the PC/Windows platform. If it can be shown
to perform adequately over a network, if it is capable of
scaling to global levels, and if the advantages of
maintaining link information separately from documents are
found clearly to outweigh the consequent difficulties, it
may become important in the future. Microcosm's authors need
to ensure that the commercialisation of Microcosm does not
hinder its adoption by the academic community.
o Hyper-G is more difficult to dismiss. It is still in a
relatively early stage of development, but appears to have
many of the necessary features. Its main disadvantages are:
(a) the lack of penetration outside the University of Graz -
the author is aware of only one other site using it; and (b)
it is currently limited to UNIX only. The author believes
that, given WWW's head start in terms of deployment, and the
current progress in adding multimedia facilities to it, WWW
stands a much better chance than Hyper-G of being accepted
as the de facto standard for distributed multimedia
applications on the Internet.
Directions for RARE
Earlier in this report, it was noted that the most important areas
where effort was needed were (a) provision of facilities for the
integrated presentation of multimedia data (including synchronisation
issues); and (b) ensuring adequate responsiveness.
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Bearing this in mind, it is recommended that RARE should invite
proposals and (subject to funding being available) subsequently
commission work to:
1. Develop conversion tools from commercial authoring packages
to WWW, and establish authoring guidelines for authors who
wish to use the conversion tools. This is a significant and
high-profile development aimed at enabling sophisticated
multimedia applications to run over the network. (Authoring
guidelines will be necessary to enable authors to fit in
with the Web's way of doing things, and to document features
of the authoring package which should be avoided because of
conversion difficulties.)
2. Implement and evaluate the most promising ways of overcoming
the QOS problem. This is an essential task without which
interactive distributed multimedia applications cannot
become a reality. Some possibilities have already been
outlined in the preceding chapter.
3. Implement a specific user project using these tools, in
order to validate that the facilities being developed are
truly relevant to actual user requirements. It may be that
partner funding from the selected user project would be
appropriate.
4. Use the experience gained from 1, 2 and 3 to inform and
influence the further development of HTML2 and HTTP2 to
ensure that they provide the required facilities.
5. Contribute to the development of the WWW clients
(particularly the Apple Macintosh and PC/MS Windows clients)
in terms of their multimedia data handling facilities.
Although it is strictly speaking outside the remit of this report
(since it is not specifically concerned with multimedia data), it is
noted that the rapid growth of WWW may in the future lead to problems
through the implementation of multiple, uncoordinated and mutually
incompatible add-on features. To guard against this trend, it may be
appropriate for RARE, in coordination with CERN and other interested
parties such as NCSA, to:
6. Encourage the formation of a consortium to coordinate WWW
technical development (protocol enhancements, etc).
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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
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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
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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
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8. Security Considerations
Security issues are not discussed in this memo.
9. Author's Address
Chris Adie
Edinburgh University Computing Service
University Library
George Square
Edinburgh EH8 9LJ
United Kingdom
Phone: +44 31 650 3363
Fax: +44 31 662 4809
EMail: C.J.Adie@edinburgh.ac.uk
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