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Abstract:

Abstract. A formal framework for the design of modular software systems is presented which incorporates the idea of reusing software components in new applications. The approach is based on structured algebraic specifications with behavioural semantics. In a first step, syntax and semantics of structured behavioural specifications are introduced. Then, in order to provide a clean interconnection mechanism for specifications, behavioural specifications with import interfaces are considered and their composition with respect to the behavioural requirements of the import interface is defined. In the next step, a simple implementation notion for behavioural specifications with import interface is presented which is compatible with the composition of specifications. Hence it is guaranteed that separately developed implementations of parts of an abstract system specification can be automatically composed to a globally correct system implementation. This is a particular important requirement for the consistent integration of reused implementations into new applications. Based on these concepts, reusable components are defined as (unordered) trees of behavioural specifications with import interfaces such that two consecutive nodes are related by the implementation relation. Hence a reusable component represents different levels of abstraction: the root of the component provides the most abstract description of the component's behaviour whereas the leaves represent different concrete implementations. A formal method for the systematic reuse of components in new applications is proposed. The method consists of four steps which describe how to construct for a given abstract system specification a modular implementation by reusing existing implementations available as leaves of appropriate reusable components. The method is demonstrated by a detailed example.

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