This paper describes the NUXMV symbolic model checker for finiteand infinite-state synchronous transition systems. NUXMV is the evolution of the NUSMV open source model checker. It builds on and extends NUSMV along two main directions. For finite-state systems it complements the basic verification techniques of NUSMV with state-of-the-art verification algorithms. For infinitestate systems, it extends the NUSMV language with new data types, namely Integers and Reals, and it provides advanced SMT-based model checking techniques.Besides extended functionalities, NUXMV has been optimized in terms of performance to be competitive with the state of the art. NUXMV has been used in several industrial projects as verification back-end, and it is the basis for several extensions to cope with requirements analysis, contract based design, model checking of hybrid systems, safety assessment, and software model checking.This work was carried out within the D-MILS project, which is partially funded under the European Commission's Seventh Framework Programme (FP7).

Contract-based design enriches a component model with properties structured in pairs of assumptions and guarantees. These properties are expressed in term of the variables at the interface of the components, and specify how a component interacts with its environment: the assumption is a property that must be satisfied by the environment of the component, while the guarantee is a property that the component must satisfy in response. Contract-based design has been recently proposed in many methodologies for taming the complexity of embedded systems. In fact, contract-based design enables stepwise refinement, compositional verification, and reuse of components. However, only few tools exist to support the formal verification underlying these methods.OCRA (Othello Contracts Refinement Analysis) is a new tool that provides means for checking the refinement of contracts specified in a linear-time temporal logic. The specification language allows to express discrete as well as metric real-time constraints. The underlying reasoning engine allows checking if the contract refinement is correct. OCRA has been used in different projects and integrated in CASE tools.

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