Designing Modal Hypermedia Applications

Different users of a hypermedia application may require different combinations of modes, i.e., different ways of perceiving the content or different ways of interaction. Multimodality - intended as the coexistence of multiple combinations of modes in the same application - can improve application richness and can accommodate the needs of different categories of users. On the other hand, multimodality increases complexity and may affect usability, since a variety of different interaction styles may be disorienting for the users. Designing an effective multimode hypermedia is a difficult problem. This paper discusses this issue, presenting a taxonomy of different kinds of modes in hypermedia applications and introducing the concept of modal hypermedia interaction. Modal interaction means that the semantics of normal application commands are dependent not only on the application state, as usual, but also on mode setting. We introduce a formal model for modal hypermedia interaction that helps us to analyze more precisely design alternatives and their impact on usability. We illustrate our approach by examples from a museum hypermedia called `Polyptych' that we actually built