A Formal Methodology for Deriving Purely Functional Programs From Z Specifications via the Intermediate Specification Language FunZ.

Abstract

In recent years, both formal methods and software reuse have been increasingly advocated as a means of alleviating the ills of the software crisis. During this same time period, purely functional programming languages, which have a long history in the realm of rapid prototyping, have emerged as a viable medium for real-world applications. Since these trends are likely to continue, this work describes a methodology that facilitates the derivation of purely functional programs from existing Z specifications. A unique aspect of the methodology is its incorporation of an intermediate specification language (FunZ) during the design phase of software development. Most of the previous techniques for translating Z specifications to functional programs were designed primarily to expedite rapid prototyping. In contrast, the FunZ methodology, which is an adapted form of the IBM Hursley method, is a comprehensive approach, spanning the software life cycle from specification through design to final implementation. Due to its greater scope, the FunZ methodology offers several advantages over existing approaches. First, the specification language integrates features from Z with those of the functional programming paradigm to provide a bridge between Z specifications and functional implementations. Since FunZ is expressly designed to target functional languages, the implementor's job is simplified. In fact, a FunZ document looks like extended Haskell code, so an obvious effect in applying FunZ is that the distance from design to code is reduced. Second, the methodology provides a framework for recording design decisions, which is useful for future maintenance. Within this framework, users may select a development path ranging from an intuitive style to a fully formal approach that includes the proofs of functional refinement. Furthermore, FunZ allows software developers to prove properties about a system design within the realm of Z or Haskell. This means that proofs can be performed throughout software development and the designer is free to select the most appropriate notation. In summary, the intermediate specification language FunZ and its related methodology provide software developers with a complete, formal approach for translating Z specifications to Haskell implementations. Previously, such extensive methods were only available for traditional, imperative languages.