An Algebraic Semantics for Contract-Based Software Components

Abstract

We propose a semantic foundation for the contract-based design of software components. Our approach focuses on the characteristic principles of component-oriented development, like provided and required interface specifications and strong encapsulation. Semantically, we adopt classical concepts of mathematical logic using models, in our framework given by labelled transition systems with “states as algebras”, sentences, and a satisfaction relation which characterizes those properties of a component which are observable by the user in the “strongly reachable” states. We distinguish between models of interfaces and models of component bodies. The latter are equipped with semantic encapsulation constraints which guarantee, that if the component body is a correct user of the required interface operations, then it can safely rely on all properties of the required interface specification. Our model-theoretic semantics of interfaces and component bodies suggests two semantic views on a component, its external and its internal semantics which must be properly related to ensure the correctness of a component. We also study a refinement relation between required and provided interface specifications of different components used for component composition.

This research has been partially supported by the GLOWA-Danube project 01LW0602A2 sponsored by the German Federal Ministry of Education and Research.