Symmetry and partial order reduction techniques in model checking Rebeca

Rebeca is an actor-based language with formal semantics that can be used in modeling concurrent and distributed software and protocols. In this paper, we study the application of partial order and symmetry reduction techniques to model checking dynamic Rebeca models. Finding symmetry based equivalence classes of states is in general a difficult problem known to be as hard as graph isomorphism. We show how, for Rebeca models, we can tackle this problem with a polynomial-time solution. Moreover, the coarse-grained interleaving semantics of Rebeca causes considerable reductions when partial order reduction is applied. We have also developed a tool that can make use of both techniques in combination or separately. The evaluation results show significant improvements in model size and model-checking time

Graph-based software specification and verification

The (in)correct functioning of many software systems heavily influences how\ud we qualify our daily lives. Software companies as well as academic computer\ud science research groups spend much effort on applying and developing techniques for improving the correctness of software systems. In this dissertation\ud we focus on using and developing graph-based techniques to specify and verify\ud the behaviour of software systems in general, and object-oriented systems more\ud specifically. We elaborate on two ways to improve the correctness (and thereby\ud the quality) of such systems.\ud Firstly, we investigate the potential of using the graph transformation tech-\ud nique to formally specify the dynamic semantics of (object-oriented) program-\ud ming languages. Those semantics are typically specified in natural language.\ud Such specifications are often hard to understand or even ambiguous. We show\ud how the graph transformation framework provides formal and intuitive means\ud for their specification.\ud Secondly, we develop techniques to verify systems of which the behaviour is\ud specified as graph production systems. For the verification of such systems, we\ud introduce an algorithm that combines a well-known on-the-\ud y model checking\ud algorithm with ideas from bounded model checking. One of the main prob-\ud lems of model checking is the state-explosion problem. This problem is often\ud tackled using partial order reduction techniques. Unfortunately, many such\ud techniques are based on assumptions that do not hold for graph production sys-\ud tems. Therefore, we develop a new dynamic partial order reduction algorithm\ud based on selecting so-called probe sets and prove its correctness.\ud Most of the techniques developed in this dissertation have been implemented\ud in the graph transformation tool GROOVE

Supporting Domain-Specific State Space Reductions through Local Partial-Order Reduction

Model checkers offer to automatically prove safety and liveness properties of complex concurrent software systems, but they are limited by state space explosion. Partial-Order Reduction (POR) is an effective technique to mitigate this burden. However, applying existing notions of POR requires to verify conditions based on execution paths of unbounded length, a difficult task in general. To enable a more intuitive and still flexible application of POR, we propose local POR (LPOR). LPOR is based on the existing notion of statically computed stubborn sets, but its locality allows to verify conditions in single states rather than over long paths. As a case study, we apply LPOR to message-passing systems. We implement it within the Java Pathfinder model checker using our general Java-based LPOR library. Our experiments show significant reductions achieved by LPOR for model checking representative message-passing protocols and, maybe surprisingly, that LPOR can outperform dynamic POR. © 2011 IEEE