Modeling railway control systems using graph grammars: A case study

Abstract

In this paper we develop in three phases a railway control system following the requirements of [2]. We are mainly concerned with the software architecture of the control system and its dynamic evolution; we do not discuss here the implementation details of the components forming the control system. First, we informally discuss our design proposal for the architecture of the control system: a hierarchy of controllers whose leaves are local controllers connected in a network that mimics the underlying railway topology. Second, we formally define by means of particular graph grammars a style of software architectures for the railway control system consisting of two complementary views and ensuring several desirable properties by construction. The dynamic evolution of the architecture is modelled by a set of coordination rules which define graph transformations and are verified with respect to to the graph grammar. Third, using a coordination rule as a formal specification of a dynamic modification of the railway control system, we derive its implementation in ConCoord, a programming environment for concurrent coordinated programming. With regard to software engineering, the two first phases belong to the system design while the third one forms the first implementation step.