HDM - A model for the design of hypertext applications

We present the latest developments of HDM, a design model for Hypertext Applications. The basic features of HDM are the representation of applications through several design primitives: typed entities composed of hierarchies of components; different perspectives for each component; units corresponding to component-perspective pairs; bodies representing the actual content of the units; structural links, binding together components or sub-entities of the same entity; typed application links, interconnecting components belonging to different entities; and a specific browsing semantics based on anchors, as a way to activate many different link types from within a unit. The development of HDM is part of the HYTEA project, carried on by a European consortium, aiming at the development of a set of authoring tools for an "engineered" development of Hypertext-Hypermedia applications. A HYTEA application is made by an HDM schema and an HDM Hyperbase (i.e., a set of instances). The basic HDM has already been shown to be translatable, either manually or through a compiler, into a node-and-link model ("a la DEXTER model"); the translated application can be targeted on several implementation tools (i.e., standard Hypertext tools already available on the market). HDM has already been used to develop a (small number) of applications, and to describe preexisting applications. These experiments have shown the need for improvements that are discussed in the paper: aggregate entities; sharing of components; is-a relationships and inheritance between entity types; sharing of bodies; structured access and "guided tours"; use of active media (animations and video-clips).