NuSMV Version 2: BDD-based + SAT-based Symbolic Model Checking

NUSMV is a symbolic model checker originated from the reengineering, reimplementation and extension of SMV [11], version 2.4.4 (SMV from now on). NUSMV has been designed to be applicable in technology transfer projects: it is a well structured, open, flexible and documented platform for model checking, and is robust and close to industrial systems standards. This paper describes the new version of NUSMV (NUSMV.2 in the following). NUSMV.2 inherits all the functionalities and the implementation style of the previous version [5] (NUSMV.1 in the following). However, NUSMV.2 significantly extends the functionalities of NUSMV.1, and its internal structure departs from the one of NUSMV.1. At the functional level, the main novelty in NUSMV.2 is the integration of model checking techniques based on propositional satisfiability (SAT). Remarkably, the integration covers the whole input language of NUSMV, and is carried out at the source code level. As far as we know, NUSMV.2 is the only publicly available system that allows for both BDD-based and SAT-based model checking. At the architectural level, a major redesign was carried out. In the new version, the functionalities provided by most modules are independent from the actual model checking engine used. Thus, for example, the services provided by the module implementing the cone of influence reduction technique can be applied both in BDD-based and SAT-based model checking. This allowed for the effective integration of the new SAT-based engine and opens up towards the integration of other model checking procedures, like the ones described in [1]. NUSMV.2 is the result of a cooperative project. IRST and the University of Trento carried out the activities related to model checking, while the University of Genova provided a package implementing reduced boolean circuits [1] and the state of the art SIM SAT solver [10]. The SIM solver is particularly effective in tackling problems arising from bounded model checking [7]. NUSMV.2 is available at http://nusmv.irst.itc.it.