“self”-conscious objects in Object-Z

Within the field of object oriented type theory, much attention has been devoted to the notion of self and Self-types. In contrast, relatively little attention has been paid to this topic in studies on object oriented specification language semantics. In the context of language semantics, the notion of self poses two problems. Firstly, it involves an awareness by an object of its own identity, and hence a capacity for self referential method invocations. Secondly, the usual reference model for object identity maps object identities to object values. This means that an object´s identity is not normally considered to be a part of its value. And so a value for self is not normally in scope. The way that a semantics resolves the scope problem can affect one´s ability to use the semantics to reason about an object independently of its environment. The paper motivates the inclusion of a concept of self in object oriented formal specification languages, and shows how this concept can be accommodated within the semantics of Object-Z. We show that a useful consequence of making objects `self´-aware is that messages between objects can be `tagged´ with the identity of the sender object; this facilitates the task of reasoning about object interaction