Module Composition and Refinement with Applications to Protocol Conversion

Abstract

In Lam and Shankar's theory of specifications based on state transition systems, modules correspond to programs or implementations; interfaces are abstract specifications defining the services that modules provide to each other. A module that correctly implements the service defined by a given interface is said to offer the interface. This paper defines two refinement relations on module specifications. The first is a sufficient condition for safety and progress properties of one module to hold in the other; it is a slight generalization of Lam and Shankar's well-formed refinement. The second relation implies that if one module offers an interface, the other does so as well. A composition operation, permitting compatible module specifications to be combined without explicitly specifying an interface between them, is also defined.