LORETO: A Tool for Reducing State Explosion in Verification of LOTOS Programs

LOTOS is a formal speciication language for concurrent and distributed systems. Basic LOTOS is the version of LOTOS without value-passing. A widely used approach to veriication of temporal properties is model checking. Often, in this approach the formal speciication is translated into a labeled transition systems on which formulae expressing properties are checked. A problem of this veriication technique is state explosion: concurrent systems are often represented by automata with a prohibitive number of states. In this paper we show how, given a set of actions, it is possible to automatically obtain for a Basic LOTOS program a reduced transition system to which only the arcs labeled by actions in belong. The set of actions plays a fundamental role in conjunction with a temporal logic deened by the authors in a previous paper: selective mu-calculus. The reduced system with respect to preserves the truth value of all selective mu-calculus formulae with actions from the set. We act at both syntactic and semantic level. From a syntactic point of view, we deene a set of transformation rules obtaining a smaller program. On the semantic side, we deene a non-standard semantics, which dynamically reduces the transition system during generation. We present a tool implementing both the syntactic and the semantic reduction.