Composing specifications

Abstract

A rigorous modular specification method requires a proof rule asserting that if each component behaves correctly in isolation, then it behaves correctly in concert with other components. Such a rule is subtle because a component need behave correctly only when its environment does, and each component is part of the others' environments. We examine the precise distinction between a system and its environment, and provide the requisite proof rule when modules are specified with safety and liveness properties.