Abstract. This paper presents CNDFS, a tight integration of two earlier multicore nested depth-first search (NDFS) algorithms for LTL model checking. CNDFS combines the different strengths and avoids some weaknesses of its predecessors. We compare CNDFS to an earlier ad-hoc combination of those two algorithms and show several benefits: It has shorter and simpler code and a simpler correctness proof. It exhibits more robust performance with similar scalability, while at the same time reducing memory requirements. The algorithm has been implemented in the multi-core backend of the LTSMIN model checker, which is now benchmarked for the first time on a 48 core machine (previously 16). The experiments demonstrate better scalability than other parallel LTL model checking algorithms, but we also investigate apparent bottlenecks. Finally, we noticed that the multi-core NDFS algorithms produce shorter counterexamples, surprisingly often shorter than their BFS-based counterparts.

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Abstract. This article presents the results of the Model Checking Contest held within the SUMo 2011 workshop, a satellite event of Petri Nets 2011. This contest aimed at a fair and experimental evaluation of the performances of model checking techniques applied to Petri nets. The participating tools were compared on several examinations (state space generation, deadlock detection and evaluation of reachability formulae) run on a set of common models (Place/Transition and Symmetric Petri nets). The collected data gave some hints about the way techniques can scale up depending on both examinations and the characteristics of the models. This paper also presents the lessons learned from the organizer's point of view. It discusses the enhancements required for future editions of the Model Checking Contest event at the Petri Nets conference.

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Abstract. The ASCoVeCo State space Analysis Platform (ASAP) is a tool for performing explicit state space analysis of coloured Petri nets (CPNs) and other formalisms. ASAP supports a wide range of state space reduction techniques and is intended to be easy to extend and to use, making it a suitable tool for students, researchers, and industrial users that would like to analyze protocols and/or experiment with different algorithms. This paper presents ASAP from these two perspectives.

This paper presents the high level Petri nets analyzer Helena. Helena can be used for the on-the-fly verification of state properties, i.e., properties that must hold in all the reachable states of the system, and deadlock freeness. Some features of Helena make it particularly efficient in terms of memory management. Structural abstractions techniques, mainly transitions agglomerations, are used to tackle the state explosion problem. Benchmarks are presented which compare our tool to Maria. Helena is developed in portable Ada and is freely available under the conditions of the GNU General Public License.

The limited amount of memory is the major bottleneck in model checking tools based on an explicit states enumeration. In this context, techniques allowing an efficient representation of the states are precious. We present in this paper a novel approach which enables to store the state space in a compact way. Though it belongs to the family of explicit storage methods, we qualify it as semi-explicit since all states are not explicitly represented in the state space. Our experiments report a memory reduction ratio up to 95% with only a tripling of the computing time in the worst case.

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