We enrich the operational semantics of a simple process calculus with ACP-style communication with a concurrency relation, so that for every process expression there exists an associated notion of just path. We then present sufficient conditions on the communication function and the syntax of process expressions that facilitate the formulation of justness on the level of labels rather than on individual transitions, taking a designated set of signals into account. This paves the way for the formulation of liveness properties under justness assumptions in the modal $$\mu $$μ-calculus and their verification on process specifications with the mCRL2 toolset.
This paper reports on a formalisation of the semi-formal modelling language SysML in the formal language mCRL2, in order to unlock formal verification and model-based testing using the mCRL2 toolset for SysML models. The formalisation focuses on a fragment of SysML used in the railway standardisation project EULYNX. It comprises the semantics of state machines, communication between objects via ports, and an action language called ASAL. It turns out that the generic execution model of SysML state machines can be elegantly specified using the rich data and process languages of mCRL2. This is a big step towards an automated translation as the generic model can be configured with a formal description of a specific set of state machines in a straightforward manner.
We present a case study on the application of formal methods in the railway domain. The case study is part of the FormaSig project, which aims to support the development of EULYNX — a European standard defining generic interfaces for railway equipment — using formal methods. We translate the semi-formal SysML models created within EULYNX to formal mCRL2 models. By adopting a model-centric approach in which a formal model is used both for analyzing the quality of the EULYNX specification and for automated compliance testing, a high degree of traceability is achieved. The target of our case study is the EULYNX Point subsystem interface. We present a detailed catalog of the safety requirements, and provide counterexamples that show that some of them do not hold without specific fairness assumptions. We also use the mCRL2 model to generate both random and guided tests, which we apply to a third-party software simulator. We share metrics on the coverage and execution time of the tests, which show that guided testing outperforms random testing. The test results indicate several discrepancies between the model and the simulator. One of these discrepancies is caused by a fault in the simulator, the others are caused by false positives; i.e. an over-approximation of fail verdicts by our test setup.
1, arend.rensink, m.i.a.stoelinga}@utwente.nl EULYNX is an EU-level collaboration between railway infrastructure managers to standardize signaling interfaces. The main goal of EULYNX is to provide, on an EU scale, a modular and flexible railroad architecture where components can easily be exchanged. This also opens the market for specialized manufacturers that do not supply the full range of control assets, but only single components. Related to EULYNX is FormaSig, an effort to establish the safety of the EULYNX standard with mathematical rigor. In particular, one of the main objectives of FormaSig is to translate the entire EULYNX standard from the semi-formal language SysML to the formal language mCRL2. The resulting mCRL2 models will subsequently be checked for important safety requirements and used for automated testing of actual EULYNX systems. This paper presents a first case study in this direction, focusing on the EULYNX Point interface, which we have converted to an mCRL2 model. We have also derived nine safety requirements, which have all been automatically compared with the mCRL2 model. Finally, we have used the mCRL2 model to test an industrial simulator of the EULYNX Point interface fully automatically.
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