Synthesis Of Concurrent Systems Research Articles

An action refinement operator for E-LOTOS with true concurrency

Action refinement is an important operation in the hierarchical synthesis of concurrent systems. We propose an action refinement operator for E-LOTOS, a standard process-algebraic language for formal specification of real-time, concurrent and reactive systems. As the first step towards giving E-LOTOS a multitude of refinement operators supporting a variety of strategies for event relationship inheritance, we propose an operator which seems both useful and simple to implement. When the operator is applied to an E-LOTOS process, it modifies its enhanced event structure, i.e. its recently defined true concurrency model. The operator allows multiple alternative implementations even for urgent events and properly reflects the fact that gate actions of E-LOTOS processes are in the general case abstractions of distributed data generation procedures.

On the well-foundedness of adequate orders used for construction of complete unfolding prefixes

Petri net unfolding prefixes are an important technique for formal verification and synthesis of concurrent systems. In this paper we show that the requirement that the adequate order used for truncating a Petri net unfolding must be well-founded is superfluous in many important cases, i.e., it logically follows from other requirements. We give a complete analysis when this is the case. These results concern the very ‘core’ of the unfolding theory.

Synthesis of concurrent systems with many similar processes

Methods for synthesizing concurrent programs from temporal logic specifications based on the use of a decision procedure for testing temporal satisfiability have been proposed by Emerson and Clarke and by Manna and Wolper. An important advantage of these synthesis methods is that they obviate the need to manually compose a program and manually construct a proof of its correctness. One only has to formulate a precise problem specification; the synthesis method then mechanically constructs a correct solution. A serious drawback of these methods in practice, however, is that they suffer from the state explosion problem. To synthesize a concurrent system consisting of K sequential processes, each having N states in its local transition diagram, requires construction of the global product-machine having about N K global states in general. This exponential growth in K makes it infeasible to synthesize systems composed of more than 2 or 3 processes. In this article, we show how to synthesize concurrent systems consisting of many (i.e., a finite but arbitrarily large number K of) similar sequential processes. Our approach avoids construction of the global product-machine for K processes; instead, it constructs a two-process product-machine for a single pair of generic sequential processes. The method is uniform in K , providing a simple template that can be instantiated for each process to yield a solution for any fixed K . The method is also illustrated on synchronization problems from the literature.

TEMPORAL LOGICS FOR TRACE SYSTEMS: ON AUTOMATED VERIFICATION

We investigate an extension of CTL (Computation Tree Logic) by past modalities, called CTL P, interpreted over Mazurkiewicz’s trace systems. The logic is powerful enough to express most of the partial order properties of distributed systems like serializability of database transactions, snapshots, parallel execution of program segments, or inevitability under concurrency fairness assumption. We show that the model checking problem for the logic is NP-hard, even if past modalities cannot be nested. Then, we give a one exponential time model checking algorithm for the logic without nested past modalities. We show that all the interesting partial order properties can be model checked using our algorithm. Next, we show that is is possible to extend the model checking algorithm to cover the whole language and its extension to [Formula: see text]. Finally, we prove that the logic is undecidable and we discuss consequences of our results on using propositional versions of partial order temporal logics to synthesis of concurrent systems from their specifications.