Contracts and Quality Attributes of Software Components

We argue that quality attributes of a component are most often not a constant property. Muchmore, the quality of a component heavily depends on the specific usage context. Therefore, we present a specification method for contractually specified components which does not specify quality attributes as constants but as functions to be evaluated at deployment. The contribution of this paper is threefold: (a) We clarify the term “contractual use of components”, a term which is often misstated or used inconsistently in current literature. We therefore translate the “design-by-contract”-principle to components. (b) We generalise component contracts to parameterised contracts, taking the mentioned context-dependencies of components into account. (c) We finally demonstrate how parameterised contracts are used to compute the reliability of software components. Results from an empirical evaluation confirm the strong context-dependency of a component’s reliability but also show that parameterised contracts for reliability prediction are easy to specify by automated control-flow analysis.