The fair cycle detectiou problem is at the heart of both LTL and fair CTL model checking. This paper preseuts a new distributed scalable algorithm for explicit fair cycle detection. Our method combines the simplicity of the distributiou of explicitly preseuted data structure and the features of symbolic algorithm allowing for an efficient parallelisa- tion. If a fair cycle (i.e. couuterexample) is detected, theu the algorithm produces a cycle, which is in general shorter than that produced by depth-first search based algorithms, Experimental results confirm that our approach outperforms that based ou a direct implementation of the best sequential algorithm.

We describe the design of (several variants of) a local parallel model-checking algorithm for the alternation-free fragment of the µ-calculus. It exploits a characterisation of the problem for this fragment in terms of two-player games. For the corresponding winner, our algorithm determines in parallel a winning strategy, which may be employed for debugging the underlying system interactively, and is designed to run on a network of workstations. Depending on the variant, its complexity is linear or quadratic. A prototype implementation within the verification tool Truth shows promising results in practice.

We have designed a tool to simplify model checking of Erlang programs by translating Erlang into a process algebra with data, called µCRL. As a case-study for this tool we focused on a simplied locker implementation after the locker that is present in the control software of the AXD 301 switch. The translation algorithm has been developed to handle this production-like code. We use the tools accompanying CRL to generate the transition systems from the specification generated by our tool. With the Caesar/Aldebaran tool set, we verified properties for our case-study.

Abstract. The explicit-state analysis of concurrent systems must handle large state spaces, which correspond to realistic systems containing many parallel processes and complex data structures. In this paper, we combine the on-the-fly approach (incremental construction of the state space) and the distributed approach (state space exploration using several machines connected by a network) in order to increase the computing power of analysis tools. To achieve this, we propose Mb-DSolve, a new algorithm for distributed on-the-fly resolution of multiple block, alternation-free boolean equation systems (Bess). First, we apply Mb-DSolve to perform distributed on-the-fly model checking of alternation-free modal µ-calculus, using the standard encoding of the problem as a Bes resolution. The speedup and memory consumption obtained on large state spaces improve over previously published approaches based on game graphs. Next, we propose an encoding of the conformance test case generation problem as a Bes resolution from which a diagnostic representing the complete test graph (Ctg) is built. By applying Mb-DSolve, we obtain a distributed on-the-fly test case generator whose capabilities scale up smoothly w.r.t. well-established existing sequential tools. 1

Concurrent software and hardware systems play an increasing rôle in today's applications. Due to the large number of states and to the high degree of non-determinism arising from the dynamic behavior of such systems, testing is generally not sucient to ensure the correctness of their implementation. Formal specification and verification methods are therefore becoming more and more popular, aiming to give rigorous support for the system design and for establishing its correctness properties, respectively (cf. [2] for an overview). In view of the inherent complexity of formal methods it is desirable to provide the user with tool support. It is even indispensable for the design of safety-critical concurrent systems where an ad hoc or conventional software engineering approach is not justifiable. There is one particularly successful automated approach to verification, called model checking, in which one tries to prove that (a model of) a system has certain properties spec...

Boolean Equation Systems (BESs) allow to represent various problems encountered in the area of propositional logic programming and verification of concurrent systems. Several sequential algorithms for global and local BES resolution have been proposed so far, mainly in the field of verification; however, these algorithms do not scale up satisfactorily as the size of BESs increases. In this paper, we propose a distributed algorithm, called DSOLVE, which performs the local resolution of a BES using a set of machines connected by a network. Our experiments for solving large BESs using clusters of PCs show linear speedups and a scalable behaviour of DSOLVE w.r.t. its sequential counterpart. 1.

In [2] we proposed a parallel graph algorithm for detecting cycles in very large directed graphs distributed over a network of workstations. The algorithm employs back-level edges as computed by the breadth first search. In this paper we describe how to turn the algorithm into an explicit state distributed memory LTL model checker by extending it with detection of accepting cycles, counterexample generation and partial order reduction. We discuss these extensions and show experimental results.

In this work we present Zeus, a Distributed Timed Model Checker that evolves from the TCTL Model Checker Kronos [13] and that currently can handle backwards computation of reachability properties [2] over timed automata [3]. Zeus was developed following a software architecture centric approach. Its conceptual architecture was conceived to be sufficiently modular to house several features such as a priori graph partitioning, synchronous and asynchronous computation, communication piggybacking, delayed messaging and dead-time utilization. Surprisingly enough, early experiments pinpointed the difficulties of getting speedups using asynchronous versions and showed interesting results on the synchronous counterpart, although being intuitively less attractive.

We present UppDMC, a distributed model-checking tool. It is tailored for checking finite-state systems and -calculus specifications with at most one alternation of minimal and maximal fixed-point operators. This fragment is also known as L . Recently, e#cient game-based algorithms for this logic have been outlined.

Abstract. Two base algorithms are known for reachability verification over timed automata. They are called forward and backwards, and traverse the automata edges using either successors or predecessors. Both usually work with a data structure called Difference Bound Matrices (DBMs). Although forward is better suited for on-the-fly construction of the model, the one known as backwards provides the basis for the verification of arbitrary formulae of the TCTL logic, and more importantly, for controller synthesis. Zeus is a distributed model checker for timed automata that uses the backwards algorithm. It works assigning each automata location to only one processor. This design choice seems the only reasonable way to deal with some complex operations involving many DBMs in order to avoid huge overheads due to distribution. This article explores the limitations of Zeus-like approaches for the distribution of timed model checkers. Our findings justify why close-to-linear speedups are so difficult –and sometimes impossible – to achieve in the general case. Nevertheless, we present mechanisms based on the way model checking is usually applied. Among others, these include model-topology-aware partitioning and on-the-fly workload redistribution. Combined, they have a positive impact on the speedups obtained.