Application of formal methods on safety assessment and fault tolerant design

摘要

On the one hand, a probabilistic Safety Assessment aims at evaluating the Criticity of failurs during the operational life of the system. Generally, Probabilistic Safety Assessment concerns the potential hardware failures and leads to build safer system architectur. On the other hand, deterministic dependability approach aims to take Design failures into account. Most of deterministic criteria of safety related I&C systems are defined by standards (e.g. IEC231 in the nuclear field). Moreover, dedicated Safety properties can be deduced form Hazard Analysis. These Properties have to be checked to ensure a safe Design, by means of intensive testing or by means of Formal Verification. Field experiences show that performing separately these two approaches may not be sufficient: Software may not preseve its Safety Properties if its environment has not the expected behaviour [Lio96]. The main goal of the mixed dependability approach described above is to analyse the behaviour of the software even in case of hardware failures, in order to Design fault tolerant systems.