Component compatibility and substitutability are widely recognized as the main issues in Component-Based Software Engineering (CBSE). Most of existing approaches suffer from the problem of component adaptation. Indeed, components compatibility and substitutability are performed component-to-component without taking into account the context. This paper proposes a new framework where more flexible component protocols compatibility and substitutability relations that depend on the context (environment) can be defined. The proposed approach is based on the notion of component protocol's usability, that is a component such that there exists an environment ensuring the completion and/or the proper termination of the composition of the involved component protocol and that environment. Two optimistic protocols compatibility relations together with two optimistic protocols behavioral subtyping relations related to the principle of substitutability are proposed. Moreover, behavioral refinement of component protocols is studied, and a link between protocols refinement and their usability is established. The soundness of the approach is shown.
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