Handling B models in the PERF integrated verification framework: Formalised and certified embedding

Abstract

• Formal verification of system design models. • Non intrusive formal verification and validation of heterogeneous models. • Isabelle/HOL based certification of transformation of B formal models to HLL formal models. • Application to railway systems. The design of complex systems involves several design models supporting different analysis techniques for validation and verification purposes. These activities lead to the definition of heterogeneous modelling languages and analysis techniques. In this setting, meeting certification standards becomes a key issue in system engineering. Reducing heterogeneity due to the presence of different modelling languages can be addressed by providing an integrated framework in which modelling languages and techniques are formalised. In such a framework, checking the global correctness of heterogeneous models of a complex critical system becomes possible in many cases. The work presented in this paper addresses the problem of integrated verification of system design models in the context of transportation systems, in particular railway systems. It has been achieved in context of the B-PERFect project of RATP (Parisian Public Transport Operator and Maintainer) aiming at applying formal verification using the PERF approach on the integrated safety-critical models of embedded software related to railway domain expressed in a single unifying modelling language: HLL. This paper addresses the particular case of the B method. It presents a certified translation of B formal models to HLL models. The proposed approach uses Isabelle/HOL as a unified logical framework to describe the formal semantics and to formalise the transformation relation between both modelling languages. The developed Isabelle/HOL models are proved in order to guarantee the correctness of our translation process. Moreover, we have also used weak-bisimulation relation to check the correctness of each translation step. We also show that, when models are translated into this unified modelling language, it becomes possible to handle the verification of properties expressed across different models. The overall approach is illustrated through a case study issued from a railway software system: on-board localisation function. Furthermore, it discusses the integrated verification at system level.