Axiomatic treatment of processes with shared variables revisited

Abstract

Abstract The aim of this paper is to develop simple and practically useful formalisms for reasoning about processes with shared variables. Our approach is based on the axiomatic system described by Neelam Soundararajan. In contrast to that work, our formalism is first derived from a model; this guarantees soundness and completeness of the formal proof system, with respect to the model. As an additional advantage the rules become simpler than those of Soundararajan; in particular, the local assertions may freely refer to shared variables; and we remove the explicit use of the compatibility predicate. Next we augment the formalism by allowing global invariants, which may refer to shared variables (including shared histories), but with a different semantics than in the local assertions. The augmented system makes reasoning simpler in the sense that reasoning about the past is replaced by reasoning about the present. Finally we suggest a sufficiently complete set of mythical (auxiliary) variables free from embedded program structure. We demonstrate our formalism on some examples.