A general theory of action languages

We present a general theory of action-based languages as a paradigm, for the description, of those computational systems which include elements of concurrency and networking, and extend this approach to describe dist.ributed systems and also t,o describe the interaction of a system, with an environment. As part of this approach we introduce the Action Language as a common model for the class of nondeterministic concurrent programming languages and define its intensional and interaction semantics in terrors of continuous transformation of environment behavior. This semantics i.s specialized for programs with stores, and extended to describe distributed computations

On the complexity of checking semantic equivalences between pushdown processes and finite-state processes

AbstractSimulation preorder/equivalence and bisimulation equivalence are the most commonly used equivalences in concurrency theory. Their standard definitions are often called strong simulation/bisimulation, while weak simulation/bisimulation abstracts from internal τ-actions.We study the computational complexity of checking these strong and weak semantic preorders/equivalences between pushdown processes and finite-state processes.We present a complete picture of the computational complexity of these problems and also study fixed-parameter tractability in two important input parameters: x, the size of the finite control of the pushdown process, and y, the size of the finite-state process.All simulation problems are generally EXPTIME-complete and only become polynomial if both parameters x and y are fixed.Weak bisimulation equivalence is PSPACE-complete, but becomes polynomial if and only if parameter x is fixed.Strong bisimulation equivalence is PSPACE-complete, but becomes polynomial if either parameter x or y is fixed