Guiding User Interfaces Equationally

Algebraic or equational speci cations are popular due to their simplicity. We advocate that such an approach could be of use for guiding user interfaces. If a user interface design process is to be accessible to a diverse user population that include novice computer users, it has to break out of the two stage user interface design| the rst stage, where a user interface builder is used to develop the look of the interface and the second phase which requires programming the semantics in a low level language. Equational speci cations can be executed by orienting equations as left-toright rewrite rules. Visual algebraic speci cations are considered as a formalism for specifying visual languages [ UD95], where among other tools, generic syntax directed editors for constructing visual terms can be generated [ Usk94]. Algebraic speci cations, like functional languages, su er from the lack of constructs that allow interaction with an user during execution. This is a drawback for specifying languages that are interactive by nature.Also of importance is the utility of seamlessly providing the user-interface speci cation and interaction, since on the average, user interface development accounts for approximately 50% of the cost of producing an application [Gra95]. We examine the utility of extending algebraic speci cations (to handle interaction) in meeting the demands of interactive tools for visual languages and user interfaces. As a result of this extension, it is possible to provide a user de nable speci cation of a language interface itself. We concentrate on the utility of a such an extension in the presence of the generated visual term editors by using only the generic features of these term editors. We argue that interaction with a user is nothing but constructing terms in editors. Thus, during execution, the user will be presented with terms whose construction must be completed.