A Strategy to Formalize Specification and Its Application to an Advanced Railway System

Abstract

This paper proposes a novel strategy for formally analyzing functional requirements specification (FRS) and applies it to the Automatic Train Protection and Block (ATPB) system, which is proposed to reconstruct conventional rail lines in Japan. Based on the FRS in natural language, firstly, dynamic state transitions are extracted to express the operational mechanisms and determine the system parameters. A complete model of the ATPB system is then established using Unified Modeling Language (UML) to express the system structure graphically and explicitly. After achieving a common understanding, a VDM++ model is established formally to redescribe the original FRS of the ATPB system which is written in natural language (i.e. Japanese). Following that, in order to ensure internal consistency of the specification, proof obligations of the VDM++ model are discharged. Furthermore, a comprehensive testing is implemented to ensure that the FRS meets actual requirements. Finally, the system is simulated strictly in accordance with the formal specification. Without any runtime errors, collisions or derailments, the results of the simulation demonstrate the high quality and safety of the specification.