Type Checking Classes in Object-Z to Promote Quality of Specifications

Formal speciication of software requirements has been recognised as an essential ingredient to improve the quality of delivered code. When integrated with the structuring mechanisms of object-orientation, formal spec-iications can provide a powerful tool for the software developer. However, the formal speciication of particularly large systems needs to be supported by tools which assist the speciier or reader of the speciication either to understand and/or to reason about a speciication. The simplest form of reasoning is that of type checking. This paper develops a simple but useful set of rules for type checking the object-oriented formal speciication language Object-Z. Although type checkers exist for Z, at present none exist for Object-Z. The lack of a type checker for Object-Z is a hinderence to a wider and more consistent use of this speciication language as an integral component in developing high-quality software products. The construction of software conforming to a client's requirements has been a major challenge of software engineering. Formal speciication, as an important part of formal methods, has been an active area in recent years, rstly within the academic and research community and now attracting serious attention from industry. One of the most 1