SPECIFICATION STATEMENTS AND REFINEMENT

We discuss the development of executable programs from state-based specifications written in the language of first-order predicate calculus. Notable examples of such specifications are those written using the techniques Z and VDM; but our interest is in the derivation of the algorithms from which they deliberately abstract. This is, the role of a development method. We propose a development method based on specification statements with which specifications are embedded in programs - standing in for developments 'yet to be done. ' We show that specification statements allow description, development, and execution to be carried out within a single language: programs/specifications become hybrid constructions in which both predicates and directly executable operations can appear. The use of a single language - embracing both high- and low-level constructs - has a considerable influence on the development style, and it is that influence we discuss: the specification statement is described, its associated calculus of refinement is given, and the use of that calculus is illustrated.