First Steps Towards Fully Abstract Semantics for Object-Oriented Languages

摘要

A number of denotational models have been proposed for object-oriented languages. Authors of more recent models have expressed dissatisfaction with the lack of "abstractness" in earlier ones. They claim that these earlier models describe details of objects which are invisible to an external observer-in short, that they are not fully abstract. In this paper, we present a formal characterization of the visible behaviour of objects. We show that using a natural full abstractness criterion based on this definition, even more recent models of object-oriented languages are unnecessarily "concrete." We go on to present a semantics for a very simple object-oriented language based on projections of state-transition graphs for programs, and demonstrate that it is fully abstract.