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HyperGraph - A Review


HyperGraph is a project which aims to provide supporting hypermedia materials for the teaching of computer graphics. The project has beendirected by Scott Owen, Georgia State University; and has been supported by the ACM SIGGRAPH Education Committee, Georgia State University and NationalScience Foundation.

HyperGraph is a great idea: create an open collection of teaching materials, with hyperlinks to allow students (or teachers) to hop from one topic to another - with an emphasis on 'open', so that the collection can grow with contributions from many different authors. The motivation and early development is well described in Owen (1992).

There are two versions of the system: the original was created using the Guide authoring system; the material has now been translated to be available over the World Wide Web. We were asked by AGOCG to provide a critical review of HyperGraph, and to assess its potential as a tool in UK Higher Education.

Both versions (Guide and WWW) are available from the ACM SIGGRAPH Education Committee Web site: - the Guide version, which runs on a PC, is also available on CD-ROM. We looked at both versions, but readers should note that recent extensions have been made only to the WWW version and this is likely to be the focus of future work.

HyperGraph - The Structure

There are two high-level structures that can be followed by a student. The first is a table of contents, which gives a simple linear list of topics; the second is a conceptual map, which aims to provide a hierarchical structure over the material, effectively a tree that the student can traverse. There are ten maps in all, each decomposing an area into a subdivision of topics - an improvement would be to provide a single view of all the maps, to see how they link together.

The idea of conceptual maps is good: they give a nice structure to the material, guiding the student through the information space; indeed it would be possible (with effort) for a lecturer to create 'personal' conceptual maps over the same material, to direct students in a particular manner.

However in the versions of HyperGraph reviewed, there were information nodes (ie leaves of the tree) which are empty. Thus it is possible to click through five levels of the tree hierarchy (and in the Web version remember these are images that have to be transferred) - but find no information at the end-node! Also, one has no visual reminder of which nodes one has visited.

HyperGraph - The Content

The content of HyperGraph reflects the view of its main contributor, Scott Owen. He has a particular view of the subject, teaching image synthesis as a physical science. The Illumination Models route from the conceptual map follows this interpretation, and indeed gives a coherent explanation of the topic. But a lecturer would have to be aware that this approach was being followed in the material, and adjust their own material accordingly.

The material on aliasing is particularly well illustrated. It includes the images and text from the 1993 ACM SIGGRAPH Education Slide Set, edited by Rosalee Wolfe.

Other areas are less well developed: the section on graphics hardware is out of date, and degenerates into note form rather than English. The inclusion of the 'shutterbug sequence' is good - but lacks a discussion piece around it.

HyperGraph - the Presentation

As with any code, it is important to structure HTML source according to certain rules - in order to allow easy maintainability by others in the future. The HTML of HyperGraph is not of high quality: many pages do not have a title; there is no proper structure; there is no uniform style (eg heading size); the text has been arbitrarily split into lines, so there are line breaks in the middle of words which appear in the formatted HTML as spaces in the middle of words; and Greek symbols in diagrams appear as Roman characters in the text, making reading quite a challenge!

In both versions, the quality of images is variable. Some have been scanned in from books and are hard to read. In the Web version, most of them are inline, and so the student may have to wait some considerable time for the pages to be downloaded - the aliasing images are an exception, being high quality and thumbnail size inline.


HyperGraph is still very raw in places, and is some way from a polished product. There is a need for quality control. A better balance needs to be found between different aspects of the system, e.g. less clicking through layers of conceptual maps and less passive reading of large areas of text (as in the case of the section on ray tracing) where one would like as a student to be more active. There are no self-assessment questions, where students can consider what they have learned. Similar views to these were also reflected in comments made by students who reviewed the Guide version of the system - their general feeling was that the system was better as a reference tool than a teaching tool.

Yet the idea is sound, and the collection contains a lot of useful material. The author does not claim perfection, and the front page makes this absolutely clear. The present version is regarded by the author as only in 0.8 beta version. Many of the presentational issues are being addressed, and the next release will remedy many of the criticisms above (within the limitations of HTML). The use of Java to implement demonstration programs within HyperGraph will allow a more active feel to the Web version.

Thus one concludes with a mix of admiration for Scott Owen having launched such a project, and developed it thus far; frustration that the current version falls short of what might have been achieved; and anticipation that future versions will better illustrate the potential.

We believe that systems such as HyperGraph are an important step towards improving the way we teach computer graphics. Please give the Web version a try - indeed let us know how you feel. We shall be thinking over the coming months how best to establish high-quality, collaboratively developed teaching resources for computer graphics, and indeed AGOCG is sponsoring a workshop to help in this thinking. Scott Owen will be a major contributor to this workshop and we look forward to working with him towards the emergence of a next generation HyperGraph.


Owen, G S (1992) HyperGraph - A Hypermedia System for Computer Graphics Education, in Interactive Learning through Visualization (eds Cunningham, S and Hubbold, R J), p65-78, Springer Verlag.

Owen, G S (1994) Teaching image synthesis as a physical science, Computersand Graphics, Vol 18, no 3, pp305-308.

Ken Brodlie,
School of Computer Studies,
University of Leeds,

Steve Maddock,
Department of Computer Science,
University of Sheffield,