Formal specification as a design tool

The formulation and analysis of a design specification is almost always of more utility than the verification of the consistency of a program with its specification. Good specification tools can assist in this process, but have generally not been proposed and evaluated in this light. In this paper we outline a specification language combining algebraic axioms and predicate transformers, present part of a non-trivial example (the specification of a high-level interface to a display), and finally discuss the analysis of this specification.