A reflection of the growing maturity of hypermedia (here, “hypermedia” is synonymous with “hypertext”) as an area of research has been the appearance of a number of thought-provoking efforts to model different aspects of the domain. Perhaps the most influential of these models is the Dexter Hypertext Reference Model [1,2], which abstracted existing hypertext systems in order to provide a basis for description, comparison, and interchange. Other models approach the task more pedagogically, choosing not to represent all aspects of existing systems but instead to present a particular, logically consistent view of hypertext that satisfies a particular goal.

HDM (Hypertext Design Model) takes the latter approach, with the goal of supporting the specification and development of hypertext-based applications. HDM provides the means for describing an application schema, which in turn can be used to generate instances. The facilities available in the model include the concept of “perspective,” in other words, multiple representations of content (including on different presentation media) selected based on the reader’s state. The model also defines three different categories of links with different roles in the representation: links among the different perspectives, links along the structure, and “application links,” which resemble traditional hypertext links. In an application, many of these links can be derived  automatically. 

HDM can be used to model applications, giving the designers and users a better idea of what has been specified. With the provision of appropriate development tools, HDM specifications can also be used to implement applications. Indeed, this ability to simultaneously describe, document, and prototype applications is one of the strengths of such hypertext-model-based efforts.