Process model for the development of system requirements specifications for railway systems

In this paper a process model for the development of system requirements specifications for railway systems is introduced. Demands of the approval of system requirements specifications, which arise from recent European railway standards, are taken into account. The aim is to obtain a system specification, which is unambiguous and easy to understand for all parties involved and in which safety aspects are considered in detail. Correlations between the development of a precise system specification, the performance of safety relevant correctness checks and the performance of risk analysis are presented. Especially the identification, specification and formalisation of safety requirements are treated with regard to correctness checks referred to safety aspects by using model checking. It is also demonstrated how different techniques of risk analysis can be supported by a system model in diagrams of the Unified Modelling Language (UML). This work has been developed in close co-operation with the Institute of Railway Systems Engineering and Traffic Safety (IfEV), Technical University of Braunschweig, Germany within the scope of the project SafeRail (see http://www.ias.uni-stuttgart.de/projekte/saferail/)