From commercial documents to system requirements: an approach for the engineering of novel CBTC solutions

Communications-based train control (CBTC) systems are the new frontier of automated train control and operation. Currently developed CBTC platforms are actually very complex systems including several functionalities, and every installed system, developed by a different company, varies in extent, scope, number, and even names of the implemented functionalities. International standards have emerged, but they remain at a quite abstract level, mostly setting terminology. This paper presents the results of an experience in defining a global model of CBTC, by mixing semi-formal modelling and product line engineering. The effort has been based on an in-depth market analysis, not limiting to particular aspects but considering as far as possible the whole picture. The paper also describes a methodology to derive novel CBTC products from the global model, and to define system requirements for the individual CBTC components. To this end, the proposed methodology employs scenario-based requirements elicitation aided with rapid prototyping. To enhance the quality of the requirements, these are written in a constrained natural language (CNL), and evaluated with natural language processing (NLP) techniques. The final goal is to go toward a formal representation of the requirements for CBTC systems. The overall approach is discussed, and the current experience with the implementation of the method is presented. In particular, we show how the presented methodology has been used in practice to derive a novel CBTC architecture.