Practical Verification of Component Substitutability Using Subtype Relation

The flexibility which components provide for assembling applications makes them an appealing solution to many engineering problems. Its darker side is the need to exercise much greater care when replacing and upgrading components within deployed applications, to ensure their stability. Formally strong methods for substitutability checks are therefore desirable but so far, not many are practically used. This paper presents a method of checking component substitutability based on subtyping relation. It uses a representation of the subtype evaluation on different levels of the component type structure, and makes it possible to perform the checks simply by comparing this representation. Two usage scenarios are described, as well as experiences from a prototype implementation for mainstream platforms