A Framework for the Formal Verification of Networks of Railway Interlockings - Application to the Belgian Railway

Limbrée, Christophe [UCL] Pecheur, Charles [UCL] et al.

Modern railway stations are controlled by computerized systems called interlockings. In fact the middle size and large size stations usually require to use several interlockings, then forming a network of interlockings. Much research propose to verify the safety properties of such systems by means of model checking. Our approach goes a step further and proposes a method to extend the verification process to a network of interlockings. This process is known as compositional verification. Each interlocking is seen as the component of a larger system (i.e., station) and interacts with its neighbours by means of interfaces. Our first contribution comes in the form of a catalogue of elements that constitute the interfaces (as used in the Belgian railways) and associated contracts. Each interface can then be bound to a formal contract allowing its verification by the ocra tool. Our second contribution comes in the form of an algorithm designed to split the topology controlled by a single interlocking into components. The verification of a large station can therefore be achieved by verifying its constituting components and their interaction thereby tackling the state space explosion problem while providing guarantees on the whole interlocking.