Composites in a Dexter-based hypermedia framework

This paper discusses the design and use of a generic composite mechanism in the object oriented DEVISE Hypermedia (DHM) development framework. The DHM development framework is based on the Dexter Hypertext Reference Model, which introduces a notion of composite to model editors with complex or multiple types of contents. The original Dexter notion of composites is, however, insufficient to cover structural composites including or referencing other components. Thus the DHM framework has been extended with generic composite classes suited to support structures within the hypermedia network itself. The paper presents and discusses the design of the generic composite classes belonging to the STORAGE and RUNTIME layers of the framework. A central aspect of the design is that the structuring mechanism is a true composite with a collection of components as its contents rather than an atomic component with links to other components as in the classical systems such as NoteCards, Intermedia, and KMS. It is also shown how the powerful generic classes can be used to implement a variety of useful hypermedia concepts such as: hierarchy by inclusion, hierarchy by reference, virtual and computed browsers, TableTops and GuidedTours.