Cooperability in Train Control Systems: Specification of Scenarios using Open Nets

We consider the area of train control systems like the European Train Control Systems (ETCS) where several different scenarios are considered and related software components must cooperate effectively in order to achieve the desired system behavior. In order to specify operational behavior of ETCS high-level Petri net techniques have been identified as one of the most adequate formal specification techniques according to the state of the art. Petri nets can be used to describe scenarios that represent the required operational behavior of the controlled system. Unfortunately, Petri nets in the usual sense are not fully adequate to model such scenarios and to achieve cooperability. This is caused by the lack of Petri nets to interact with the environment. Thus Petri nets fail to provide a suitable notion for cooperability between different components of a system. The new notion of open nets, developed within the research group “Petri Net Technology”, is most promising as a conceptual and formal technique for these kinds of problems. In this paper we study a simplified version of a railway level crossing control system. There are a few number of basic scenarios represented by interaction diagrams, which are modeled by open nets, called scenario nets. The cooperability of system components is ensured by suitable integration and composition techniques for open nets. These techniques provide a basis for cooperability in train control systems in general, especially for problems in the area of ETCS.