rightly contends that the view, held by many hypermedia researchers
and implementors, that the network is simply a transparent data
highway which needs no special consideration in application design,
is wrong. It is argued that:
"the very same structural characteristics that may make
a multimedia document appealing to the end user are the
characteristics that are extremely helpful during
dynamic network performance optimisation".
This is a particularly relevant statement considered in the light of
suggestion 5 above.
6.3. Recommended Further Work
To meet the needs of applications such as those described in section
2.1, the community must seek where possible to adapt and enhance
existing tools, not to build new ones. There is now an opportunity
for RARE to stimulate and encourage this process of adaptation and
enhancement, and the following subsections outline a strategy for
this.
Selecting a System
In order to have the greatest effect, RARE should concentrate its
efforts on only one of the existing tools. Candidate technologies
are those already outlined: Gopher, WWW, WAIS, Hyper-G, Microcosm and
AthenaMuse 2.
It is recommended that RARE should select the World-Wide Web to
concentrate its efforts on. The reasons for this decision are as
follows.
o Flexibility. The rich yet straightforward design of WWW,
with its clearly separable components (HTML, URL and HTTP),
means that it is a very flexible basis on which to develop
distributed multimedia applications.
o Existing efforts. The WWW implementor community is already
discussing and designing extensions to HTML (HTML2),
intended (among other things) to support multimedia. There
is clearly much interest in this area, and RARE efforts
could complement existing work.
o Hyperlinks. A clear requirement of many applications is the
availability of hyperlinking, which WWW supports well.
o Integrated solution. Because WAIS, Gopher and Hyper-G (as
well as anonymous FTP servers) may all be accessed from Web
clients, WWW serves as an important integrating tool for
information services. It is important that distributed
multimedia applications, which require extensive support in
the client software, should be based on a technology "close
to" such integrated clients.
o Penetration and growth. Although Gopher far surpasses WWW
in the number of servers available, the rate of growth in
WWW usage is greater than that of Gopher. There is an
increasing realisation in the community that Gopher is over-
simplistic for many purposes, and a corresponding increase
in interest in WWW.
o Attention to QOS issues. There is already an awareness in
the WWW community of the need for achieving an appropriate
QOS, and a mechanism has already been proposed in HTTP2 to
alleviate the problem.
o Standardisation. The WWW team is taking standardisation of
the existing WWW system components seriously. The URL
format has already been published as an Internet draft (and
has been adopted as an important component of the proposed
Internet integrated information infrastructure), and the
current version of HTML is about to follow suit. The use of
SGML as the basis of HTML complies with the perceived
importance of SGML for hypermedia in general (and also fits
in with RARE's approach of adopting appropriate open
standards).
o Software status. CERN has recently placed the WWW code
developed by it into the public domain. This is unlike all
the other candidate technologies, which all have
restrictions on who can do what with the code. In the case
of Gopher, these restrictions are already causing some
commercial users to look at other options.
WWW has two significant disadvantages, both of which are being
alleviated:
o Restricted choice of client software. At present, Apple
Macintosh and PC/MS Windows clients are available in beta
form only. By contrast, there are more than one well-tested
Gopher clients available for these platforms.
However, other WWW clients for the Mac and MS Windows are in
the pipeline.
o There is a perception in the community that making
information available over HTTP is difficult, and that it
must be put into HTML.
However, it is possible to put plain-text, non-HTML
documents onto the Web. Such documents of course cannot
contain links.
Furthermore, WYSIWYG HTML text editors are available, to
ease the pain of writing HTML.
The main disadvantages of the other systems are:
o Gopher is designed for simplicity, and therefore lacks the
flexibility of WWW. In particular its structure is too
inflexibly hierarchical and it does not have hyperlinks.
Its main advantage is its very heavy penetration. However,
because of the WWW approach to accessing data using other
protocols, all of gopherspace is part of the Web. Any Web
client should be able to be a gopher client too.
It is neither envisaged that Gopher will go away, nor that
it won't be used for multimedia data. However, Gopher is
unlikely to be used for more sophisticated multimedia
applications such as academic publishing, interactive
multimedia databases and CAL, because of the above-mentioned
limitations.
o WAIS is a specialised tool, and will certainly form part of
the overall solution, particularly for database-type
applications. It is not a general solution for distributed
hypermedia applications.
o AthenaMuse 2 is commercially-oriented: it is clear that
academic and research users will have to pay to use the
software. Its level of use is thus very unlikely to be as
great as publiclyavailable systems such as WWW. Moreover,
it does not support all the required platforms.
o Microcosm network support is still in early stages, limited
at present to the PC/Windows platform. If it can be shown
to perform adequately over a network, if it is capable of
scaling to global levels, and if the advantages of
maintaining link information separately from documents are
found clearly to outweigh the consequent difficulties, it
may become important in the future. Microcosm's authors need
to ensure that the commercialisation of Microcosm does not
hinder its adoption by the academic community.
o Hyper-G is more difficult to dismiss. It is still in a
relatively early stage of development, but appears to have
many of the necessary features. Its main disadvantages are:
(a) the lack of penetration outside the University of Graz -
the author is aware of only one other site using it; and (b)
it is currently limited to UNIX only. The author believes
that, given WWW's head start in terms of deployment, and the
current progress in adding multimedia facilities to it, WWW
stands a much better chance than Hyper-G of being accepted
as the de facto standard for distributed multimedia
applications on the Internet.
Directions for RARE
Earlier in this report, it was noted that the most important areas
where effort was needed were (a) provision of facilities for the
integrated presentation of multimedia data (including synchronisation
issues); and (b) ensuring adequate responsiveness.
Bearing this in mind, it is recommended that RARE should invite
proposals and (subject to funding being available) subsequently
commission work to:
1. Develop conversion tools from commercial authoring packages
to WWW, and establish authoring guidelines for authors who
wish to use the conversion tools. This is a significant and
high-profile development aimed at enabling sophisticated
multimedia applications to run over the network. (Authoring
guidelines will be necessary to enable authors to fit in
with the Web's way of doing things, and to document features
of the authoring package which should be avoided because of
conversion difficulties.)
2. Implement and evaluate the most promising ways of overcoming
the QOS problem. This is an essential task without which
interactive distributed multimedia applications cannot
become a reality. Some possibilities have already been
outlined in the preceding chapter.
3. Implement a specific user project using these tools, in
order to validate that the facilities being developed are
truly relevant to actual user requirements. It may be that
partner funding from the selected user project would be
appropriate.
4. Use the experience gained from 1, 2 and 3 to inform and
influence the further development of HTML2 and HTTP2 to
ensure that they provide the required facilities.
5. Contribute to the development of the WWW clients
(particularly the Apple Macintosh and PC/MS Windows clients)
in terms of their multimedia data handling facilities.
Although it is strictly speaking outside the remit of this report
(since it is not specifically concerned with multimedia data), it is
noted that the rapid growth of WWW may in the future lead to problems
through the implementation of multiple, uncoordinated and mutually
incompatible add-on features. To guard against this trend, it may be
appropriate for RARE, in coordination with CERN and other interested
parties such as NCSA, to:
6. Encourage the formation of a consortium to coordinate WWW
technical development (protocol enhancements, etc).
7. References
[1] "A Survey of Distributed Multimedia Research,
Standards and Products", ed. C. Adie, January 1993
(RARE Technical Report 5).
URL=ftp://ftp.ed.ac.uk/pub/mmsurvey/
[2] "The Dexter Hypertext Reference Model", F. Halasz and
M. Schwartz, NIST Hypertext Standardisation Workshop,
January 1990.
[3] "Response Time and Display Rate in Human Performance
with Computers", B. Shneiderman, Comp. Surveys 16,
1984.
[4] "Gopher+: Proposed Enhancements to the Internet
Gopher Protocol", B. Alberti, F. Anklesaria, P. Linder,
M. McCahill, D. Torrey, Summer 1992.
URL=gopher://boombox.micro.umn.edu:70/11/gopher/gop
her_protocol/Gopher%2b
[5] "WAIS Interface Protocol", F. Davies, B. Kahle, H.
Morris, J. Salem, T. Shen, R. Wang, J. Sui and M.
Grinbaum, April 1990.
URL=ftp://quake.think.com/wais/doc/protspec.txt
[6] "Uniform Resource Locators", T. Berners-Lee, March
1993. URL=ftp://info.cern.ch/pub/ietf/url4.ps
[7] "The HTTP Protocol as Implemented in W3", T. Berners-
Lee, January 1992.
URL=ftp://info.cern.ch/pub/www/doc/http.txt
[8] "Protocol for the Retrieval and Manipulation of
Textual and Hypermedia Information", T. Berners-Lee,
1993. URL=ftp://info.cern.ch/pub/www/doc/httpspec.ps
[9] "Hypertext Markup Language (HTML)", T Berners-Lee,
March 1993. URL=ftp://info.cern.ch/pub/www/doc/html-
spec.ps
[10] "Hyper-G: A Universal Hypermedia System", F. Kappe and
N. Sherbakov, March 1992. URL=ftp://iicm.tu-
graz.ac.at/pub/HyperG/doc/report333.txt.Z
[11] "Towards an Integrated Information Environment with
Open Hypermedia Systems", H. Davis, W. Hall, I. Heath,
G. Hill, Proceedings of the ACM Conference on
Hypertext, Milan 1992, p181-190.
[12] "The AthenaMuse 2 Functional Specification", L.
Bolduc, J. Culbert T. Harada, J. Harward, E.
Schlusselberg, May 1992.
URL=ftp://ceci.mit.edu/pub/AM2/funcspec.txt.Z
[13] "Research and Technology Development in Advanced
Communications Technologies in Europe: RACE '92",
CEC, March 1992. Available from:
raco@postman.dg13.cec.be
[14] "Esprit Programme Synopses", CEC, October 1992. In
seven volumes. Available from
esprit_order_mailbox@eurokom.ie
[15] "CMIFed: A Presentation Environment for Portable
Hypermedia Documents", G. van Rossum, J. Jansen, K. S.
Mullender, D. C. A. Bulterman, Amsterdam 1993 (also
presented at ACM Multimedia 93 conference).
URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9305.ps.Z
[16] "The Amsterdam Hypermedia Model: extending hypertext
to support real multimedia", L. Hardman, D. C. A.
Bulterman, G. van Rossum, Amsterdam 1993
URL=ftp://ftp.cwi.nl/pub/CWIreports/CST/CSR9306.ps.Z
[17] "Deja-Vu Distributed Hypermedia Application
Framework", A. Eliens.
URL=ftp://ftp.cs.vu.nl/eliens/Deja-Vu-proposal.ps
[18] "Bento Specification", J. Harris and I. Ruben, Apple
Computer Inc, August 1992.
URL=ftp://ftp.apple.com/apple/standards/Bento_1.0d4.1
[19] "Davenport Advisory Standard for Hypermedia (DASH),
Module I: Standard Open Formal Architecture for
Browsable Hypermedia Documents (SOFABED)", ed S. R.
Newcomb and V. T. Newcomb.
URL=ftp://sgml1.ex.ac.uk/davenport/sofabed.0.9.6.ps.Z
[20] Article in comp.text.sgml newsgroup, 24 May 1993, by
Eliot Kimber (drmacro@vnet.ibm.com).
URL=ftp://ftp.ifi.uio.no/SGML/comp.text.sgml/by.msg
id/19930524.152345.29@almaden.ibm.com
[21] "Emerging Hypermedia Standards" B. Markey, Multimedia
for Now and the Future (Usenix Conference
Proceedings), June 1991.
[22] "Initial Draft PREMO (Presentation Environment for
Multimedia Objects", ISO/IEC JTC1/SC24 N847, November
1992.
[23] "Recommended Practices for Multimedia Portability",
Release 1.1 October 1990, Interactive Multimedia
Association, 3 Church Circle, Suite 800, Annapolis,
MD 21401-1993, USA.
[24] "Recommended Practices for Enhancing Digital Audio
Compatability in Multimedia Systems", Release 3.00
1992, Interactive Multimedia Association, 3 Church
Circle, Suite 800, Annapolis, MD 21401-1993, USA.
[25] "RIFF Tagged File Format", Microsoft Inc, 1992.
[26] "A Vision of an Integrated Internet Information
Service", C. Weider and P. Deutsch, March 1993,
Work in Progress.
[27] "Delivering Interactive Multimedia Documents over
Networks", S. Loeb, IEEE Communications Magazine, May
1992.
[28] "A Status Report on Networked Information Retrieval:
Tools and Groups", ed. J. Foster, G. Brett and P.
Deutsch, March 1993.
URL=ftp://mailbase.ac.uk/pub/nir/nir.status.report
8. Security Considerations
Security issues are not discussed in this memo.
9. Author's Address
Chris Adie
Edinburgh University Computing Service
University Library
George Square
Edinburgh EH8 9LJ
United Kingdom
Phone: +44 31 650 3363
Fax: +44 31 662 4809