Electronic Proceedings of the
ACM Workshop on Effective Abstractions in Multimedia
November 4, 1995
San Francisco, California
Model Based Approaches to Hypermedia Design
The advantages of model-based approaches to hypermedia applications building have been shown elsewhere. [Garzotto93], [Isakowitz94]. To briefly summarize the important concepts behind model-based design we can say that a design model for hypermedia applications provides a predefined vocabulary of concepts and primitives which can be used to specify them, with little regard for the content of the nodes. The use of a model helps to discipline the authoring activity so that:
- Large hypermedia will not be built "on the fly". (Scheme definition as in database design is important).
- Conceptual relationships among nodes will be described before node instantiation.
- Navigational structures and patterns will be formally specified before instantiation.
- The interface and interaction structure will be specified in an implementation-independent way.
Existing design models extend the hypermedia data model with higher level constructs, providing conceptual tools for building abstractions (in the sense of data abstractions, where implementation is not only hidden but also relegated to a further step). In HDM [Garzotto93] for instance, a hypermedia scheme is described as a set of entity types and their relationships (application links); entities are composed of (hierarchically structured) components, and each component may be viewed in different perspectives using Units (the HDM equivalent to hypermedia nodes). RMD [Balasubramaniam94] extends HDM by adding richer index and guided tours structures.
We have extended HDM ideas by adopting some well known object oriented concepts (mainly the specification of structure, behavior and class inheritance) and by defining a step-by-step process comprising conceptual, navigation and interface design. The model presented in this paper provides a framework for representing knowledge about the conceptual structure of hypermedia documents, their content and presentation. Being object oriented it could be a starting point for making hypermedia applications more modular and in the mid-term for building a theoretical basis for reuse of hypermedia elements.