Abstract. We present a capability calculus for checking partial confluence of channel-communicating concurrent processes. Our approach automatically detects more programs to be partially confluent than previous approaches and is able to handle a mix of different kinds of communication channels, including shared reference cells. 1

Abstract. Due to the significant progress in automated verification, there are often several techniques for a particular verification problem. In many circumstances different techniques are complementary — each technique works well for different type of input instances. Unfortunately, it is not clear how to choose an appropriate technique for a specific instance of a problem. In this work we argue that this problem, selection of a technique and tuning its parameter values, should be considered as a standalone problem (a verification meta-search). We propose several classifications of models of asynchronous system and discuss applications of these classifications in the context of explicit finite state model checking. 1

Abstract. State space explosion is the hardest challenge to the effective application of model checking methods. We present a new technique for achieving drastic state space reductions that can be applied to a very wide range of concurrent systems, namely any system specified as a rewrite theory. Given a rewrite theory R = (Σ, E, R) whose equational part (Σ, E) specifies some state predicates P, we identify a subset S ⊆ R of rewrite rules that are P-invisible, so that rewriting with S does not change the truth value of the predicates P. We then use S to construct a reduced rewrite theory R/S in which all states reachable by S-transitions become identified. We show that if R/S satisfies reasonable executability assumptions, then it is in fact stuttering bisimilar to R and therefore both satisfy the same CT L ∗ −X formulas. We can then use the typically much smaller R/S to verify such formulas. We show through several case studies that the reductions achievable this way can be huge in practice. Furthermore, we also present a generalization of our construction that instead uses a stuttering simulation and can be applied to an even broader class of systems. 1

Abstract. In order to apply formal methods in practice, the practitioner has to comprehend a vast amount of research literature and realistically evaluate practical merits of different approaches. In this paper we focus on explicit finite state model checking and study this area from practitioner’s point of view. We provide a systematic overview of techniques for fighting state space explosion and we analyse trends in the research. We also report on our own experience with practical performance of techniques. Our main conclusion and recommendation for practitioner is the following: be critical to claims of dramatic improvement brought by a single sophisticated technique, rather use many different simple techniques and combine them. 1

confluence is a reduction technique used in exolicit state model-checking of labeled transition systems to avoid the state explosion problem. In this report, we propose a new on-the-fly algorithm to calculate partial #-confluence, and propose new techniques to do so on large systems in a compositional manner. Using information inherent in the way a large system is composed of smaller systems, we show how we can deduce partial #-confluence in a computationally cheap manner. Finally, these techniques are applied to a number of case studies, including the rel/REL atomic multicast protocol.

Abstract not found

Abstract. We present a new method for fighting the state space explosion of process algebraic specifications, by performing static analysis on an intermediate format: linear process equations (LPEs). Our method consists of two steps: (1) we reconstruct the LPE’s control flow, detecting control flow parameters that were introduced by linearisation as well as those already encoded in the original specification; (2) we reset parameters found to be irrelevant based on data flow analysis techniques similar to traditional liveness analysis, modified to take into account the parallel nature of the specifications. Our transformation is correct with respect to strong bisimilarity, and never increases the state space. Case studies show that impressive reductions occur in practice, which could not be obtained automatically without reconstructing the control flow. 1

Abstract—This paper presents a novel linear processalgebraic format for probabilistic automata. The key ingredient is a symbolic transformation of probabilistic process algebra terms that incorporate data into this linear format while preserving strong probabilistic bisimulation. This generalises similar techniques for traditional process algebras with data, and — more importantly — treats data and data-dependent probabilistic choice in a fully symbolic manner, paving the way to the symbolic analysis of parameterised probabilistic systems. Keywords-probabilistic process algebra, linearisation, datadependent probabilistic choice, symbolic transformations I.

Abstract. We present a probabilistic leader election algorithm for anonymous, bidirectional, asynchronous rings. It is based on an algorithm from Franklin [22], augmented with random identity selection, hop counters to detect identity clashes, and round numbers modulo 2. As a result, the algorithm is finite-state, so that various model checking techniques can be employed to verify its correctness, that is, eventually a unique leader is elected with probability one. We also sketch a formal correctness proof of the algorithm for rings with arbitrary size. 1

Abstract: It is desirable to integrate formal verification techniques applicable to different languages. We present Exp.Open 2.0, a new tool of the Cadp verification toolbox which combines several features. First, Exp.Open 2.0 allows to describe concurrent systems as a composition of finite state machines, using either synchronization vectors, or parallel composition, hiding, renaming, and cut operators from several process algebras (Ccs, Csp, Lotos, E-Lotos, µCrl). Second, together with other tools of Cadp, Exp.Open 2.0 allows state space generation and on-the-fly exploration. Third, Exp.Open 2.0 implements on-the-fly partial order reductions to avoid the generation of irrelevant interleavings of independent transitions. Fourth, Exp.Open 2.0 allows to export models towards other tools using interchange formats such as automata networks and Petri nets. Finally, we show some practical applications and measure the efficiency of Exp.Open 2.0 on several benchmarks. Key-words: Concurrent system, compositional verification, enumerative verification, explicit state verification, labelled transition system, model checking, on-the-fly verification, parallel composition, partial order reduction, process algebra, synchronization vector