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Using formal specifications in the design of a human-computer interface

Formal specification techniques are valuable in software development because they permit a designer to describe the external behavior of a system precisely without specifying its internal implementation. Although formal specifications have been applied to many areas of software systems, they have not been widely used for specifying user interfaces. In the Military Message System project at the Naval Research Laboratory, the user interfaces as well as the other components of a family of message systems are specified formally, and prototypes are then implemented from the specifications. This paper illustrates the specification of the user interface module for the family of message systems. It then surveys specification techniques that can be applied to human-computer interfaces and divides the techniques into two categories: those based on state transition diagrams and those based on BNF. Examples of both types of specifications are given. Specification notations based on state transition diagrams are preferable to those based on BNF because the former capture the surface structure of the user interface more perspicuously. In either notation, a high-level abstraction for describing the semantics of the user interface is needed, and an application-specific one is used here.