Interface as a basic concept for systems specification and verification

To specify or to verify a system means to prescribe or to analyze its connections with the environment into which it shall be or in which it is embedded. From this point of view, its internal construction and its internal behaviour are relevant only as far as they determine its communication and cooperation with the outside. Hence, both specification and verification are concerned with a part of the system only, namely its interface with its environment. As a basis to deal with such partially determined systems, an appropriate means to represent them and a suitable equivalence notion are needed. This paper discusses the use of strictly labelled net systems for the representation of system interfaces and the notion of interface equivalence. The latter notion is a generalization of bisimulation and is intended to preserve the most important properties of sytems at the interface with their environment. It can constitute a basis for deriving concepts of compatibility to be used in answering the question whether and to what extent a realized system fulfills a given specification.