Using Formal Methods for Verification and Validation in Railway.

A very promising and efficient method of showing the correctness of a complex system is using formal methods on a model of that system. To this end there exist plentiful methods and tools for easing the mathematically burdensome process of refinement and proofs, as well as the computationally complex task of model checking. While in todays industrial applications formal methods are mostly used for verification (i.e. for showing that the system model fulfills properties such as completeness and consistency) we propose to use these methods for validation as well (i.e. correspondence of the model with the customer needs). In this paper we show the applicability as well as the limitations of this approach for feature driven development towards continuous verification and validation. As an example we present a model of a railway interlocking system written in Event-B. The model can be instantiated and animated, which in combination with model checking and formal proofs demonstrates the usefulness of the approach. The resulting model can be used again to automatically generate test cases which are suitable to show the correspondence of the implementation and the model, given that the model supports a sufficient level of detail.