Inheritance and subtyping in a parallel object-oriented language

Abstract

We have investigated the concepts of inheritance and subtyping in order to integrate them in a parallel object-oriented language. In doing so, we have concluded that inheritance and subtyping are two different concepts, which should not be confused in any object-oriented language (be it parallel or sequential). Inheritance takes place on the implementation level of classes, and it is a convenient mechanism for code sharing. It can be supported, for example, by introducing inheritance packages into a programming language. Subtyping deals with the message interface of objects, and it leads to a conceptual hierarchy based on behavioural specialization. Subtyping should take place on the basis of specifications of the external behaviour of objects, and as much as possible of these specifications should be formal. Some specific problems with introducing these two concepts into a parallel language are also discussed.