Design Support for Hypermedia Documents

Abstract

The nonlinear nature of hypermedia documents makes them notoriously difficult to describe. Consequently design prior to implementation is a challenging task. This paper examines design issues specific to hypermedia, and describes the development of HANDlE, a notation for the description of the structural organisation of hypermedia documents. HANDlE is based on a directed graph approach, but it incorporates a range of abstractions which provide significant simplification, and which allow the underlying structure of a document to remain clearly visible. The evaluation of a prototype design environment based on HANDlE is described, and range of refmements for the future are proposed. Because of their inherent nonlinearity, hypermedia documents are very difficult to describe; in fact, their best description is usually their implementation. As a consequence, attempting to carry out comprehensive organisational and structural design prior to implementation is a challenging task. The majority of hypermedia design aids available are either (i) style guides, relating to appearance and frarne-toframe relationships, providing little to support the overall design of the document or system, or (ii) are inextricably tied into a particular formal design methodology. The development and extraordinarily rapid penetration of the World-Wide Web has highlighted the need for tools to assist with WWW site design and maintenance, where the bulk ofthe issues involved are generic to hypermedia. This need is further exacerbated by the fact that many of those engaged in the design cf hypermedia systems and WWW sites have little or no formal background in software systems design (Pohl and Purgathofer, 1994). This paper examines the critical problems of hypermedia design which set it apart from more conventional software development, and reviews a range of current design tools. From this base, a graphical notation for the description of hypermedia systems is then developed, aimed specifically at supporting the hypermedia design process rather than prescribing a formal design methodology. The prototype implementation of this notation within a hypermedia design environment (HANDlE) is described. Some preliminary feedback from designers who have evaluated the system is also discussed. HYPERMEDIA DESIGN ISSUESDesigning hypermedia documents is a complex activity. Nanard and Nanard (1995) identifY the need for formal tools to reduce the cognitive load on the document designer, and to reduce the level of complexity in the design process. One approach is to provide the user with abstract semantic types which can be used to describe a complex real-world situation in a relatively simple fashion. For example, EntityRelationship (ER) modelling is used in traditional software design with the provision of abstract types in the form of entities and relationships at the simplest level, followed by more complex semantic constructs such as aggregation and specialisation at higher levels (Chen, 1976). Another approach to reducing complexity is to allo...