Model-Based Verification of Safety Contracts

The verification of safety becomes crucial in critical systems where human lives depend on the correct functioning of such systems. Formal methods have often been advocated as necessary to ensure the reliability of software systems, albeit with a considerable effort. In any case, such an effort is cost-effective when verifying safety-critical systems. Safety requirements are usually expressed using safety contracts, in terms of assumptions and guarantees. To facilitate the adoption of formal methods in the safety-critical software industry, we propose the use of well-known modelling languages, such as UML, to model a software system, and the use of OCL to express the system safety contracts within UML. A UML model enriched with OCL constraints is then transformed to a Petri net model that enables to formally verify such safety contracts. We apply our approach to an industrial case study that models a train doors controller in charge of the opening and closing of train doors. Our approach allows to perform an early safety verification, which increases the confidence of software engineers while designing the system.