Executable specifications for a human-computer interface

TL;DR: A specification technique for user interfaces based on state transition diagrams, based on a non-deterministic model, is introduced and then demonstrated for a secure message system application.

Abstract: It is useful to be able to specify a proposed human-computer interface formally before building it, particularly if a mockup suitable for testing can be obtained directly from the specification. A specification technique for user interfaces, based on state transition diagrams, is introduced and then demonstrated for a secure message system application. An interpreter that executes the resulting specification is then described. Some problems that arise in specifying a user interface are addressed by particular features of the technique: To reduce the complexity of the developer's task, a user interface is divided into the semantic, syntactic, and lexical levels, and a separate executable specification is provided for each. A process of stepwise refinement of the syntactic specification, leading from an informal specification to an executable one is also presented. Since the state diagram notation is based on a non-deterministic model, constraints necessary to realize the system with a deterministic interpreter are given.