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We aim at improving the performance of distributed algorithms for model checking and state space reduction. To this end, we introduce a new distribution policy of states over workers. This policy reduces the number of transitions between states located at different workers. This in turn is expected to reduce the communication costs of the distributed algorithms.The main idea is to use Abstract Interpretation techniques to compute a small approximation of the state space, starting from some high level description of the system. Based on this approximation, the connectivity of concrete states is predicted. This information is used to distribute states with expected connectivity to the same worker. Experiments show a considerable reduction of cross transitions, at the expense of a modest unbalance of nodes per worker.

The logic of equality and uninterpreted functions (EUF) has been proposed for processor verification. This paper presents a new data structure called Binary Decision Diagrams for representing EUF formulas (EUF-BDDs). We define EUF-BDDs similar to BDDs, but we allow equalities between terms as labels instead of Boolean variables. We provide an approach to build a reduced ordered EUF-BDD (EUF-ROBDD) and prove that every path to a leaf is satisfiable by construction. Moreover, EUF-ROBDDs are logically equivalent representations of EUF-formulae, so they can also be used to represent state spaces in symbolic model checking with data.

We describe a framework to generate modal abstract approximations from process algebraic specifications, written in the language µCRL. We allow abstraction of state variables and action labels. Moreover, we introduce a new format for process specifications called Modal Linear Process Equation (MLPE). Every transition step may lead to a set of abstract tates labelled with a set of abstract actions. We use MLPEs to characterize abstract interpretations of systems and to generate Modal Labelled Transition Systems, in which transitions may have two modalities may and must. We prove that the abstractions are sound for the full action-based µ-calculus. Finally, we apply the result to check some safety and liveness properties for the bounded retransmission protocol.

We present an efficient algorithm to determine the maximal class of confluent Τ -transitions in a labelled transition system. Confluent Τ -transitions are inert with respect to branching bisimulation. This allows to use Τ -priorisation, which means that in a state with a confluent outgoing Τ -transition all other transitions can be removed, maintaining branching bisimulation. In combination with the removal of Τ-loops, and the compression of Τ-sequences this yields an efficient algorithm to reduce the size of large state spaces.

In this paper we propose a uniform description of basic BDD theory and algorithms by means of term rewriting. Since a BDD is a DAG instead of a tree we need a notion of shared rewriting and develop appropriate theory. A rewriting system is presented by which canonical forms can be obtained. Various reduction strategies give rise to different algorithms. A layerwise strategy is proposed having the same time complexity as the traditional apply- algorithm, and the lazy strategy is studied, which resembles the existing up-one-algorithm. We show that these algorithms have incomparable performance.