Formal definitions of behavioural compatibility for active and passive objects

The modular refinement of object-oriented specifications requires a sound theory of behavioural compatibility of classes. Such a theory will depend on the way in which objects of a class interact with their environment. This paper defines two notions of behavioural compatibility. Observational compatibility is relevant when an active object is placed within a passive environment and operational compatibility when a passive object is placed in an active environment. Rules for maintaining each type of behavioural compatibility through inheritance are also presented