Always and Eventually in Object Requirements

Object oriented models and methods encompass a set of techniques which have been, and will continue to be, applied in the successful production of complex software systems. The methods are based on the simple concepts of abstraction, encapsulation, classification and polymorphism. The formal verification of logical properties of such models is difficult to integrate into the traditional operational view. Furthermore, most, if not all, of the object oriented formalisms are based on the specification of safety properties and, as such, they do not provide an adequate means of expressing liveness conditions. We examine a mixed semantic framework in which a state-based object oriented semantics is extended with the concepts of always and eventually. These semantics have been integrated to provide a set of re-usable fair object templates whose graphical representation can be formalised by the client for use during synthesis and analysis of their requirements. Proof of invariant and eventuality properties is done by translation to PVS and TLA, respectively. The utility of such an approach is illustrated through a simple telephone feature case study.