Weak subtyping-yet another notion of inheritance

Reuse in polymorphic systems strongly depends on correct use of inheritance. There have been many efforts to check whether or not subtyping is correct. All of these approaches either restrict the use of inheritance customize the class hierarchies in an application specific way or use proof theoretical techniques. This is often too restrictive or even impossible-at least for practical use. In order to provide both flexibility and robustness the paper introduces the concept of weak conformance. This concept allows the specification of specialized classes that may be used in a polymorphic context. The main idea is to check conformance in the context of a concrete application. Furthermore, the paper demonstrates how the proposed concept can easily be integrated into any programming language and introduces an algorithm for checking robustness of an application. This algorithm detects all critical and illegal polymorphic method calls that may violate the robustness. Finally the paper discusses ways of handling critical calls, i.e., calls that can be proven correct by the developer but not by the type system