The Hyper-G Network Information System
Keith Andrews, Frank Kappe, and Hermann Maurer
( Institute for Information Processing and Computer Supported New Media (IICM)
Graz University of Technology
A-8010 Graz, Austria.
As the Internet continues to experience exponential rates of growth,
attention is shifting away from mainstream network services such as
electronic mail and file transfer to more interactive information
services. Current network information systems, whilst extremely
successful, run into problems of fragmentation, consistency,
scalability, and loss of orientation.
The development of 'second generation' network information systems
such as Hyper-G can help overcome these limitations. Of particular
note are Hyper-Gs tightly-coupled structuring, linking, and search
facilities, its projection of a seamless information space across
server boundaries with respect to each of these facilities, and its
support for multiple languages. The Harmony client for Hyper-G
utilises two and three-dimensional visualisations of the information
space and couples location feedback to search and link browsing
operations, in order to reduce the likelihood of disorientation. This
paper presents a comprehensive overview of Hyper-G and Harmony.
Hypermedia, information system, information
visualisation, graphical interaction, Internet.
The Internet, the world-wide computer network, now connects more than
3.8 million individual computers (October 1994) with a growth rate of
between 10-15% per month [Network Wizards 1994]. More than 18
terabytes of information traversed the NSFNET, the main US backbone of
the Internet, in the month of September 1994 [Merit NIC 1994]. Whilst traditional services such as
electronic mail, remote login, and file transfer (FTP) still account
for the bulk of Internet traffic, by far the fastest growth is being
experienced by network information systems like WAIS, Gopher, and the
These three information systems have transformed the way people
perceive and interact with information resources on the net. All
three are client-server applications using the Internet's underlying
TCP/IP protocol: end-users run client software (available for a wide
variety of platforms) which communicates over the network with servers
managing access to a vast amount of extremely diverse information.
WAIS (Wide Area Information Servers), began in 1989 as a joint
development of Thinking Machines, Apple Computer, and Dow Jones to
provide on-line access to the Wall Street Journal [Kahle et al. 1992]. WAIS supports powerful content-based search of (previously) indexed
databases, including relevance feedback by which (parts of)
text documents returned by a search and deemed to be particularly
relevant by the user are used as input for a subsequent search,
effect refining the search by asking WAIS to look for further similar
documents. WAIS is purely a search engine, it supports neither
associative browsing (hyperlinks) nor any structuring of its
Gopher was started in 1991 as a campus-wide information system at the
University of Minnesota [McCahill and Anklesaria 1995] [Anklesaria et al. 1993]. It provides
menu-like access to information resources. Although Gopher space is in
fact a graph containing many loops, the menu presentation gives the
impression of a tree. Typically, users begin navigation at the top of
the tree and traverse down to leaf nodes containing actual data. One
sub-tree on each server usually contains a menu of other Gopher
servers. Gopher has no integrated search facilities of its own, but
provides access to optional add-on search engines such as WAIS; it has
no provision for hyperlinks.
The World-Wide Web project (WWW, W3, or simply 'The Web') was
initiated at CERN, Geneva, in 1989, originally as an information
system for the particle physics community [Cailliau 1995] [Berners-Lee et al. 1994]. W3 is a
distributed hypermedia system: combining the concept of
hyperlinks (associative browsing by following links to related
information) with multimedia (text, image, audio, video,
etc.). Through its URL (Universal Resource Locator) mechanism, W3 can
represent links to any document on any W3, Gopher, or FTP server
worldwide. The CGI script interface allows W3 servers to start
arbitrary application programs, for example linking into external
databases or implementing complex search algorithms. Simple,
intuitive W3 clients such as Mosaic and Netscape have contributed to
its tremendous current popularity.
However, W3 has a number of limitations. It does not provide any
information structuring facilities beyond hyperlinks; its links are
one-way (there is no way of determining which other documents refer to
a particular document, leading to inconsistencies when documents are
moved or deleted -- the frequent 'dangling links') and embedded
within text documents (there are no links from other kinds of
documents). Like Gopher, W3 has no native search facilities, but
relies on external search engines such as WAIS, leading to patchy
server-by-server provision of search facilities by individual sites
and no real-time cross-server searches (searches in previously
generated cross-server indices are available). The flexibility
provided by CGI is achieved at great cost: the uniformity of the
interface disappears, different W3 servers behave differently --
resulting in the 'Balkanisation' (to quote Ted Nelson) of the Web
into independent 'W3 Empires'. Also, there is little support for the
maintenance of large datasets, so it is not uncommon to see several W3
servers within a single organisation, each a fundamentally separate
interactive context. The Web today is very much 'read-only', in the
sense that information providers prepare data sets in which
information consumers can generally only browse. Finally, although its
URL mechanism endows W3 with scalability in terms of number of
servers, it is not scalable in terms of number of users. Extremely
popular W3 servers such as Sun Microsystems' World Cup USA '94
[Sun Microsystems] site can often become overwhelmed by tens of
thousands of users, necessitating their physical mirroring to many
WAIS, Gopher, and W3 belong to the first generation of information
systems on the Internet [Fenn and Maurer 1994]. They work well in
particular contexts but run into difficulties when applied to hundreds
of thousands of documents distributed over many thousands of servers.
They provide no graphical navigation aids, only rudimentary access
control, little support for automatic database
scalable document replication mechanisms, and little support for
multiple languages. In the rest of this paper we describe Hyper-G, a
second generation system designed to transcend some of the limitations
of existing environments.
Hyper-G is a multi-user, multi-protocol, structured, hypermedia
information system, which runs as a client-server application on the
Internet [Andrews and Kappe 1994],[Andrews et al. 1994], [Kappe 1993].
2.1 Design Goals
Based on an analysis of the strengths and weaknesses of existing
systems, the following primary design goals were formulated:
1. Provide orientational and navigational aids.
2. Provide automatic structuring and maintenance.
3. Reduce fragmentation across servers.
4. Support user identification and access control.
5. Support multilinguality.
6. Maintain interoperability with existing systems.
To help alleviate the disorientation associated with becoming 'lost
in hyperspace', Hyper-G provides three closely coupled, orthogonal
navigational mechanisms: structuring, hyperlinks, and search. The
tight coupling allows clients to correlate search results, link maps,
and structure overviews, providing a powerful aid to navigation.
Users of W3 are soon confronted with the 'dangling link' syndrome
inherent in W3's data model: when a document is moved or deleted,
there is no way of automatically updating or deleting links to that
document - following such links produces an error message. In
Hyper-G, the consistency of links is maintained automatically by the
server, as are Hyper-Gs aggregate structures.
To counter the Balkanisation of databases, Hyper-G provides much
functionality integrated into it (and hence uniform in nature) which
has to be implemented on top of W3 or Gopher (and hence potentially
differing from site to site), in particular powerful search and
retrieval facilities which can be performed simultaneously and
seamlessly across server borders. Information can also be
structured both within and across server borders.
In order to differentiate between users and provide tailored views of
the available information, support at the system level for user
accounts, user groups, access rights, and access modes is essential.
They are also a prerequisite for the implementation of charging
All of the currently popular Internet information systems are more or
less implicitly bound to a single language: English. Although the
Gopher+ and W3 protocols in theory support multi-language versions of
documents, most clients do not use these facilities. Similarly,
elements in the user interface are relatively easily translated to
other languages, but most clients support only a single interface
language; the same applies to full text search in multiple languages.
Hyper-G and its clients, on the other hand, were specifically designed
for multilingual use.
Figure 1: The Hyper-G Data Model
Hyper-G was designed to overcome the limitations of existing tools
like WAIS, Gopher, and W3, while at the same time maintaining
interoperability with them - interoperability was considered crucial
to the acceptance of a system in today's multi-protocol Internet.
2.2 Design Features
The most fundamental design decision was to provide support for
orthogonal yet closely coupled structuring, linking, and search
facilities at the database level (as shown in Figure 1):
- Structuring: Documents may be grouped into aggregate collections, which may themselves belong to other
collections. Every document must belong to at least one collection.
Navigation may be performed down through the collection hierarchy
(the collection 'hierarchy' is, strictly speaking, a directed
acyclic graph), access rights assigned on a collection-by-collection
basis, and the scope of searches restricted to particular sets of
collections. Collections may span multiple Hyper-G servers,
providing a unified view of distributed resources.
- Linking: Hyperlinks connect a source anchor
within one document to either a destination anchor within
another document, an entire document, or a collection. Links are not stored within documents (as in W3) but in a separate link database
(as pioneered by Intermedia [Haan et al. 1992]. This has a number of
- (*) Source and destination anchors are not limited to text
documents, but can be attached to any kind of media (image, audio,
film, 3D scene, formatted PostScript document, etc.).
- (*) Links can be attached to otherwise read-only documents (for
example documents on CD-ROM or with read-only access rights).
- (*) Links can be followed backwards.
- (*) A local map (fish-eye view) can be readily computed and
visualised using the link database.
- (*) Consistency constraints can be met more easily (for example
when moving or deleting a document, it is important to know which
other documents contain links to it).
- Attribute and Content Search: Documents and collections
have an associated set of attributes (author, title, keywords, etc.)
which may be searched for, including boolean combinations and term
truncation. Full text (content) search facilities include vector and
fuzzy boolean queries. Every document and collection is
automatically indexed upon insertion into the database - no extra
indexing steps are required. The scope of a search may be focussed
to one or more collections on one or more servers or may be as wide
as all collections on all Hyper-G servers worldwide.
Each of these three orthogonal features work seamlessly across
server boundaries, reducing fragmentation while at the same time
promoting consistency. To achieve scalability in terms of number of
users, Hyper-G servers replicate and cache remote objects; updates are
propagated to other servers using an efficient, scalable flooding
algorithm [Kappe 1995].
A special kind of collection, a cluster, groups documents into
logical entities. Clusters are used both to define multimedia
aggregates (for example, a text and an associated image or video clip)
which are presented together and multilingual aggregates (for example,
English and German translations of a text, audio clip, structure
diagram, or any combination of these).
Other design features supported by Hyper-G and not found in comparable
- Anonymous and identified user identification modes.
- A scheme of user groups and subgroups maintained by the server.
- Access rights for users and user groups on a document or
- 'Home collections', personal information spaces for identified
users (kept on the server) used to organise personal documents and
pointers to resources.
- Language preferences, applied both to document retrieval and to
the user interface.
- An underlying object-oriented database, which guarantees the
consistency and integrity of data (for example the updating of links
when a document is moved or deleted).
Figure 2 shows the architecture of Hyper-G. Note the
interoperability of Hyper-G with Gopher and W3 clients and servers.
When accessed by a Gopher client, the Hyper-G server maps the
collection hierarchy into a Gopher menu tree (hyperlinks cannot be
represented in Gopher). A synthetic search item is
Figure 2: The Architecture of Hyper-G
generated at the
foot of each Gopher menu to allow searching the corresponding
collection. When accessed by a W3 client, each level of the collection
hierarchy is converted to an HTML [Berners-Lee and Conolly 1993] document containing a
menu of links to its members. Hyper-G text documents are transformed
on-the-fly into HTML documents, including any links they might have.
Additional Hyper-G functionality such as user identification, language
preference selection, and searching are implemented via HTML forms and
are accessible at any time.
The Hyper-G server is able to store pointers to remote objects on
Gopher and W3 servers. This allows the incorporation of information on
remote non-Hyper-G servers (almost) seamlessly: Gopher menus are
transformed into Hyper-G collections and W3 text documents into
Hyper-G text documents. Interoperability with WAIS (Z39.50) and FTP
servers is planned.
Unlike Gopher or W3 clients which connect to many servers during a
typical session, Hyper-G clients talk to a single Hyper-G server for
the entire session. Should information from a remote server be needed,
the local server acts as a proxy, i.e. it fetches the object and
passes it on to the client. This approach has the following
- Clients are kept simple, the Hyper-G server handles external protocols.
- Remote information can be cached in the local server.
- User accounts and access rights have only to be maintained on the local server (the user has to identify to one server only).
- Statistics and user profile information can be gathered on a per-session basis.
Hyper-G clients connect to a Hyper-G server using the assigned port
number 418 by default. Port 418 is used for control information,
Figure 3: The Architecture of the Harmony Client for Hyper-G
generally sent (simultaneously in the case of multimedia
clusters) using dynamically assigned port numbers. The precise
mechanism is described in the Hyper-G Client/Server Protocol (HG-CSP)
specification [Kappe and Pani 1994].
3 The Harmony Client for Hyper-G
Harmony is the native Hyper-G client for X Windows on Unix platforms.
It takes advantage of Hyper-Gs underlying facilities to provide
intuitive navigational tools and informative feedback about the
location of information.
As can be seen in Figure 3, Harmony is a multi-process
application: the primary process, the Session Manager,
communicates with the Hyper-G server, provides navigational
facilities, and coordinates all other activities. The session manager
starts secondary processes, document viewers, as necessary to
display particular documents. Native Harmony document viewers conform
to the Harmony Document Viewer Protocol (DVP) [Andrews et al. 1995],
which defines various browsing, editing, and link functions. There
currently exist native document viewers for text, images, MPEG films,
audio, 3D scenes, and PostScript. Harmony may be configured to run
external programs in place of any native viewer and also for
unsupported document types (the document is piped to standard input),
however without provision for link activation and editing.
Figure 4 shows a typical Harmony session. The Session
Manager (top left) provides navigation through the collection
structure, search facilities, and various general functions such as
user identification and language selection. Collections
Figure 4: Harmony - The Hyper-G Client for X Windows
may be opened and closed and clusters or individual documents
activated within the
graphical collection display by double-clicking. Collections,
clusters, or documents which have already been visited are marked with
a tick. In this example, a descriptive text and an image about the
city of Graz have been accessed.
The Harmony Text Viewer (top right) uses a generic SGML parser to
display marked-up text documents (both Hyper-Gs HTF and W3's HTML
formats), and has the usual facilities for scrolling, finding strings,
selecting, etc. Hyperlinks within the text can be highlighted in a
number of ways. Inline images in TIFF, GIF, and JPEG formats are
The Harmony Image Viewer (bottom right) accepts raster images in a
variety of common formats (TIFF, GIF, JPEG, etc.). Operations such as
zooming and panning are available. Link anchors are rectangular,
circular, or elliptical (soon also polygonal) areas, which are
overlaid atop the image. All Harmony document viewers support both
interactive link following and definition.
Harmony's Film Player (not shown) displays MPEG (MPEG-1, soon MPEG-2)
video streams. It is possible to define a link anchor which follows an
object of interest in the video: rectangular and circular anchor
regions overlaying the film are simply defined for specific keyframes
(they are interpolated in between
keyframes). Anchors can be activated
both during playback and while playback is paused. The Harmony Audio
Player (not shown) can be configured to use either the Network Audio
Server [Fulton and Renda 1994] or local audio commands to play audio files in a variety of common formats.
The Local Map facility (bottom left), provides a kind of short-range
radar, generating on request (dynamically) a map of the link
relationships of a chosen document, similar to the local map of
Intermedia [Haan et al. 1992]. By default, two levels of incoming and
outgoing hyperlinks are represented. One can navigate within the local
map by selecting (single-clicking) another object toward the edge of
the map and generating a new display. Objects can be activated by
The language preference dialogue (centre) allows the user to specify
an ordered list of preferred languages. Harmony's user interface
adjusts dynamically to the language of first choice (English and
German interfaces are currently supported), documents available in
multiple languages are selected in order of language preference, and
searches are optionally language-dependent.
Central to the design of Harmony is the concept of location
feedback. When a document or collection is visited, its location
within the collection structure is automatically displayed in the
Session Manager's collection browser (by opening up the path to it),
regardless of whether the object was reached as the result of a
search, by following a hyperlink, or via the local map. This unique
feature of Harmony is a powerful instrument in the fight against
becoming 'lost in hyperspace' - users can orient themselves with
reference to a fixed structural framework. In the case of search
results and the local map, mere selection of an object initiates
location feedback, providing users with a sense of the context of an
object, prior to any decision to view it.
The Harmony search dialogue (not shown) provides an interface to the
full range of Hyper-G searches: attribute and content, boolean and
fuzzy. The scope of a search may be focussed to a single collection or
set of specific collections (possibly spanning server boundaries), or
may be as wide as all collections on the local server. Search results
are presented as a ranked list. As noted above, Harmony applies the
principle of location feedback to search results: selecting an object
in the result list causes its location in the collection structure to
be displayed, hence users can make informed choices before committing
to fetch particular documents.
A further innovative feature of Harmony is its use of
three-dimensional visualisations, both hand-crafted and automatically
generated [Andrews 1993], [Andrews and Pichler 1994]. Model description files representing
arbitrarily complex scenes or objects are displayed by the Harmony 3D
Scene Viewer. Figure 5 shows the scene viewer displaying a
model of the Great Hall of the Austrian National Library (top left)
and a staute of Kaiser Karl VI (bottom left). Users typically view a
model of a scene by moving themselves (walk, fly, fly to, heads-up)
and view a model of an object by moving the model (translate, rotate,
zoom). 3D models are fully-fledged hypermedia documents: hyperlinks
may be attached to individual objects within a scene or to groups of
polygons within an object.
Harmony's Information Landscape, also shown in Figure 5, is an
interactive, three-dimensional visualisation of the collection
structure, tightly coupled to the Session Manager's two-dimensional
collection browser display (changes in one are reflected in the
other). The collection hierarchy is mapped out onto a plane, documents
within a collection are arranged on top of the corresponding block;
Figure 5: Harmony Landscape and 3D Scene Viewer
colour and height are used to encode document type and size
respectively. Users can 'fly' over the landscape looking for salient
features, like flying over a file system with FSN [Tesler and Strasnick 1992]. A flat overview window (upper right) provides a further aid to
orientation. Through their ability to compactly display many thousands
of objects, 3D visualisations are perhaps the only effective means of
browsing in and judging the extent of large, dynamic information
The Harmony PostScript Viewer (Figure 6) displays
arbitrary documents in PostScript format; the documents are typically
stored and transmitted in compressed form and uncompressed locally by
the viewer. Rectangular link anchors are supported.
As was mentioned in the opening discussion, Hyper-G clients can be
used to edit as well as browse the contents of a Hyper-G
server, in so far as the user is identified and has appropriate access
rights. Figure 7 shows the Harmony Insert Dialogue
being used to upload a text document about Graz from the local file
system into the user's home collection. Figure 8 shows
a link being created from the word Styria in the text about Graz to a
multimedia cluster about the Austrian Province of Styria.
Figure 6: The Harmony PostScript Viewer
Finally, Harmony's History Browser (not shown) offers a timeline of
past interactive waypoints, including previous search panels --
another means of orienting in hyperspace.
Features to be implemented in Harmony over the coming months include
interactive forms, a drag-and-drop interface to the local file system
(allowing documents to be simply pulled into collections on the
server), integrated electronic mail facilities, semi-automatic link
generation, and three-dimensional representations of hyperlink
relationships and search results. An immersive (virtual reality)
interface is also planned.
4 Concluding Remarks
We have presented the design rationale and the current development
status of Hyper-G and its Harmony client for X Windows. Of particular
note are Hyper-Gs tightly-coupled collection, link, and search
facilities, its projection of a seamless information space across
server boundaries, and its support for multiple languages. Harmony
makes innovative use of location feedback and two
Figure 7: The Harmony Insert Dialogue
Figure 8: The Harmony Link Creator
Figure 9: Accessing a Hyper-G Server with Mosaic
and three-dimensional visualisations to help users navigate and orient
themselves within large, dynamic information spaces.
A key design goal of Hyper-G was to maintian interoperability with
current information systems. The combination of the Hyper-G server's
rich structuring and maintenance facilities and its ability to service
requests from W3 and Gopher clients in addition to native Hyper-G
clients make it ideal for use as a multi-protocol server.
Figure 9 shows the Mosaic client for W3 being used to
access the J.UCS collection on the IICM's Hyper-G server.
Although still in its infancy, Hyper-G has already gained considerable
acceptance. The European Space Agency and the Museum of New Zealand
have adopted Hyper-G for their own information systems, the Austrian
Ministry of Science has adopted it as its information system of choice
for all Austrian universities, and the German Mathematics Association
(DMV) is setting up an information system spanning most German
universities and colleges, to name just a few examples.
Hyper-G also is being used as the basis for a major new electronic
publishing venture. The Journal of Universal Computer Science (J.UCS),
supported by Springer Verlag, is among the first high-quality,
scientific journals to depend primarily
on Internet distribution [Maurer and Schmaranz 1994]. The pilot issue is already available at several sites, the first regular issue will be available world-wide at the end of January 1995.
In addition to the Harmony client described in this paper, native
Hyper-G clients are available for Unix VT100-style terminals (hgtv)
and MS-Windows (Amadeus), and a client is under development for the
Macintosh. Further information about Hyper-G and Harmony and
installation details may be retrieved by anonymous ftp from
ftp.iicm.tu-graz.ac.at in directory /pub/Hyper-G or from the
IICM Information Server under http://info.iicm.tu-graz.ac.at/ or
Financial support of Hyper-G by the Austrian Ministry of Science,
JOANNEUM RESEARCH, and the European Space Agency is gratefully
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