Merging State-Based and Action-Based Verification

A formalism is presented that is intended to combine basic properties of both state-based and action-based verification. In state-based verification the behaviour of the system is described in terms of the properties of its states, whereas action-based methods concentrate on transitions between states. A typical state-based approach consists of representing requirements as temporal logic formulae, and model-checking the state space of the system against them. Action-based verification often consists of comparing systems according to some equivalence or preorder relation. We add state propositions to a typical process-algebraic action framework. Values of state propositions are propagated through process-algebraic compositions and reductions by augmenting actions with changes of proposition values. A modified parallel composition operator is used for synchronisation of processes and handling of state propositions. Efficient on-the-fly verification is obtained with four kinds of rejection conditions. The formalism is implemented in a new verification tool TVT.