A Comparison of WWW and Hyper-G
University of Hagen, Germany
Abstract: In this paper we attempt to compare features of
WWW and Hyper-G, the first fully operable networked multimedia system
that goes much beyond WWW and incorporates many features first
proposed in Xanadu and later partially tested in systems such as
Keywords: Hypermedia, Hyper-G, WWW, Xanadu,
networked information systems, Internet
Although WWW has become a major buzz word in connection with the
Information Superhighway it was originally designed for limited size
information system applications. As it is being used for more and more
diverse and large efforts it is become increasingly clear that more
powerful tools are necessary.
Although not yet as widely known, one such tool has emerged in 1995
that deserves attention: its compatibility with WWW combined with a
more sophisticated architecture and many desperately needed features
is making Hyper-G one of the obvious candidates to take over where WWW
reaches its limits.
This paper is an attempt to present a comparison between the two
systems and indicate why we believe WWW is less suitable for large or
2 Data Representation
a) The native text representation format for WWW is HTML, which is
evolving through a series of official versions (1.0, 2.0 and now 3.0)
and a range of of proprietary extensions implemented in browsers from
companies such as IBM, Microsoft and Netscape. Hyper-G uses HTF
(Hyper Text Format) and HTML. Both HTML and HTF are applications of
HTML and HTF have many similarities, although HTF has more powerful
hyperlinks which may overlap while HTML has forms for user interaction
and is being extended with a variety of interesting presentation
facilities. Neither is suitable for scientific publishing, as they do
not support the advanced type control necessary to present formulae,
resulting in many authors currently resorting to inline images of the
desired typography! HTML 3.0 will support mathematical notation.
b) Other text formats: both WWW and Hyper-G servers can support a
variety of other text formats which can then be presented by viewing
software either integrated into the browser or externally invoked as a
"helper application". The existing native Hyper-G browsers already
support Postscript (and can support hyperlinks on the Postscript
documents). Internal support for Adobe PDF (Portable Document Format)
and HTML in the Hyper-G browsers is in development.
c) The future: WWW is firmly committed to HTML, with gradual adoption
of HTML 3.0 as the standard begins to coalesce although additional
proprietary tags will no doubt continue to complicate the issue,
perhaps to be included in later revisions of the HTML standard.
Hyper-G will add HTML 3.0 support by the end of 1995, including
tables, forms and CGI (Common Gateway Interface) scripts, thus
providing full compatibility with WWW.
2.2 Other Data
a) Both WWW and Hyper-G servers and viewers support images in GIF and
JPEG format, both inline and as documents in their own right.
b) Both WWW and Hyper-G servers and viewers support audio and video
clips. There is no mechanism to support hyperlinks within audio and
video objects in WWW. Only the entire media object can be a link
destination. Hyper-G permits links to and from sections of audio and
c) 3D scenes are supported in both WWW and Hyper-G using the VRML
3 Data Structures
3.1 Basic Units
WWW: documents; Hyper-G: clusters of documents which are intended to
be presented simultaneously or represent the same information in
different forms, for example in different languages. The WWW concept
is a special case of the Hyper-G version when a cluster contains only
3.2 Structuring of Documents
WWW: no structuring beyond (uni)directional links; thus, a WWW
database has no well-defined document groupings other than the server
filesystem directory structure, which is therefore often used to
define the scope for searches and access authorisation. This requires
considerable planning and maintenance of the server filesystem layout.
Hyper-G: bi-directional links; clusters have attributes (that can be
searched on) and are grouped into collections. Collections can
themselves be members of other collections, and may belong to more
than one parent collection; thus, Hyper-G provides two orthogonal
structuring paradigms, elements of a relational database and hence a
variety of access techniques.
4 Link Philosophy
4.1 Basic Links
WWW: links are uni-directional and embedded into documents. They can
be attatched to text or images, but not to other media. The
destination is generally an entire document but may also be a position
within the document or (with some servers) a byte range within a
Hyper-G: links are bi-visible and bi-followable, stored in a separate
link database, can be associated with any part of text, image, audio
and video material and can have as destination a collection, a
document or part of a document.
Hyper-G is more flexible in its link concept: the bi-visibility makes
it possible to determine all documents pointing to any given document
(particularly important for database maintenance!); keeping links in a
separate server database from the documents allows users to add their
own private links even to documents they do not own ("construction of
private views and customization"); links to no longer existing
documents can be easily removed; source and destination anchors in
Hyper-G are generalisations of the WWW concept.
4.2 Forms and Clickable Imagemaps
WWW supports forms that can be filled out and "clickable
imagemaps". In clickable imagemaps a cursor position can be returned
and used in an arbitrary program. Since Hyper-G inherently supports
source anchors for links on regions of an image, it can provide the
same functionality without additional programming at the server. This
is similar to the new "USEMAP" HTML tag which defines the image
regions for the browser. Hyper-G will also support HTML forms.
5 Server Philosophy
5.1 Network of Servers vs. Distributed Database
WWW: Users access one server at a time and switch from server to
server using a "stateless" protocol. Each document request generates
a separate connection to the server where that document is stored,
possibly via a proxy server.
Hyper-G: Users access one server and through that server all others,
unless explicitly overruled. This makes it much easier to generate
statistics on user navigation through the server.
The Hyper-G approach allows extensive caching: when 100 persons
access, through a local Hyper-G server X, a picture from a remote
server Y that picture will be transfered from Y to X only a single
time; in WWW the picture will be transmitted from Y to each of the 100
persons unless those persons all point their clients to a proxy server
with caching running. The Hyper-G server-server protocol also ensures
cache consistency, which is a difficult issue with WWW proxy caches.
The fixed connection approach of Hyper-G has one potential drawback:
suppose a New Yorker accesses a Hyper-G server in Paris and finds a
link there to another New York server. In WWW selecting this link
by-passes Paris immediately; in Hyper-G the user has to explicitly
disconnect with the Paris server if
the "detour" is considered
undesirable. It may, however, be desirable since billing services and
disciplined use of the Internet become easier using this Hyper-G
5.2 Integration of Other Servers
WWW provides a common Gateway Interface (CGI) to integrate external
applications; a similar interface has been announced for Hyper-G. SQL
gateways (Oracle, Sybase, etc.) have also been implemented for
WWW has no built-in search facility. Some WWW servers such as WN do
have built in searching, and most allow third-party search engines
such as WAIS or GLIMPSE to be added. However, this requires
additional configuration and is implemented differently (if at all) on
There are also various search engines that index documents from as
many WWW servers as possible, such as Lycos, Webcrawler and Excite.
However, these indexes are built by programs which laboriously "crawl"
around the WWW following links to discover documents, and thus often
contain many documents which no longer exist or have been moved. Many
documents are not indexed because they have not been discovered by the
Hyper-G has a built-in search facility: as search scope a union of
collections (even distributed over geographically distant servers) can
be specified. Attribute, title and full-text searches are supported.
WWW servers are available from CERN, NCSA, NetScape, and others. Most
platforms are supported.
Hyper-G servers are available under UNIX (including Linux) and have
been announced for Windows NT. Hyper-G is freely available, and
maintenance contracts for commercial users are provided. Sources are
available but have to be licensed for commercial usage.
"Secure" servers are available from NCSA (S-HTTP) and Netscape (SSL
and S-HTTP). Hyper-G has pledged to follow the NCSA approach to
provide authentication, security and privacy, and to have additonal
Hyper-G offers two ways for billing information right now: a
"subscription" approach based on passwords and a "limited number of
users at a time" licensing technique.
In Hyper-G users can "annotate" documents (by adding their own linked
documents), and annotations can themselves be annotated. Since viewers
support the annotation process this provides for an asynchronous
computer conferencing feature not available in WWW (where the embedded
link concept does not allow this kind of annotation).
5.7 "Local" Database
A "local" server that allows previously downloaded documents to be
viewed is available in rudimentary form for Netscape. A powerful
version has been announced for Hyper-G. Thus, parts of Hyper-G
databases can be directly transferred to CD-ROM. The ED-MEDIA'95
proceedings available under
<http://hyperg.iicm.tu-graz.ac.at/electronic_library> is one example:
it is available in exactly the same form also on a CD.
6 Clients and Interoperability
A host of WWW clients are available on the PC, Mac and Unix platforms.
The best known are NCSA Mosaic and Netscape. The latter has achieved
some 70% market share within the last six months. Netscape is easy to
install and to use, fast, and offers a number of features like access
to Newsgroups and FTP that other viewers (including Hyper-G viewers)
are still lacking.
For Hyper-G there is the "Terminal Viewer" HGTV, a simple text-based
viewer and editor for all platforms, the fancy X-Windows viewer
Harmony and the MS-Windows viewer Amadeus. Both Harmony and Amadeus
have navigational features going beyond WWW clients (see 6.2. below)
and can be used as powerful structure-editing tools. A particularly
easy to use "one-window" viewer for Hyper-G under MS-Windows is in
preparation. A Mac viewer is also under development.
6.2 Navigational Features
All clients (WWW and Hyper-G) provide basic navigational facilities
like "back", "history", "bookmark", clicking on a link, etc. The
extent of navigational facilities depends also on the server. Hence,
Hyper-G viewers give "location feedback" (showing where users are
within the collections of Hyper-G), a "local map" (showing in- and
outgoing links, currently only supported by Harmony) and "3D
Information landscapes" (Harmony only). Navigational features for
Hyper-G even with WWW clients include search facilities and "go to
parents of current collection": these features are provided to
non-Hyper-G clients in the Hyper-G WWW gateway.
All WWW viewers allow access to Hyper-G servers (and profit in this
case from some of Hyper-G's functionality). Conversely, all Hyper-G
viewers allow access to all WWW servers. Note that 100% compatibility
even between WWW clients is impossible as long as HTML 3.0 is not
universally accepted as standard.
However, it is important to understand that the choice of viewer is
independent of the choice of server.
7 Penetration And Developments
WWW has literally exploded during the last 2 years. Numbers vary, but
some 20,000 servers are installed, albeit the vast majority containing
not more then a few pages. Hyper-G (server and Harmony viewer) was
released in January 95, causing some ripples. By mid 1995, over 100
Hyper-G servers are installed with remarkable growth. WWW is better
suited for small applications, but Hyper-G is the only viable
alternative for large databases when WWW (without much "propping up")
tends to break down.
Some main players at the moment are:
(1) NCSA working on server and client (Mosaic) development.
(2) IICM/IHM Graz working on Hyper-G.
(3) Netscape working on Netscape servers and clients.
(4) University of Minnesota working on the next generation Gopher
(5) CERN, the original home of WWW, working on standardisation,
particularly of HTML 3.0.
(6) INRIA, which just has entered the arena to take over some of the
work CERN has previously been doing.
The W3 Consortium, headed by MIT with INRIA its European partner, is
trying to channel new developments; and so is the recently formed Web
Society (see <http://info.websoc.at/>), where members of IICM/IHM
Graz, UMN, CERN and INRIA have become directors, with NCSA potentially
to follow. The directors of the Web Society (in contrast to W3C) must
come from non-profit organisations.
NCSA, IICM/IHM Graz, UMN, and CERN are in close coordination to assure
interoperability on the viewer level now and in the future; they will
also try to join forces with INRIA.
As a first cooperative venture a VRML Viewer has recently been jointly
announced by NCSA, IICM/IHM Graz and UMN. These organisations have
also agreed on further joint development work on future integrated
Internet tools combining the best of Gopher, WWW, and Hyper-G.
The IICM/IHM Graz and UMN are cooperating closely on the client side
and on providing Gopher users an upgrade path to Hyper-G.
A Hyper-G consortium has been formed. Details can be found at
<hyperg://hyperg.hgc.org/> or <http://www.hgc.org/>.
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