iStar Goal Model to Z Formal Model Translation and Model Checking of CBTC Moving Block Interlocking System

Abstract

The reliability and safety of complex software systems are provided by extracting safety requirements from regulations and operational environments and later specifying these requirements precisely. At the early stage, these extracted safety requirements are informal. Typically, they cope with non-functional requirements. Analysis of early requirements using traditional methods is inadequate because these methods only focus on the WHAT dimension of requirements engineering but do not address the WHY dimension of requirements engineering. In this article, we are using a goal-oriented modelling method called iStar to confront these issues. To ensure that the software system developed fulfils the requirements specified in the early-phase, it is necessary to integrate early-phase requirements with late-phase requirements. To accomplish this task, in this article, we use Z formal method to integrate early-phase requirements with late-phase requirements. This integration synergistically resolves the above issues. As a case study, we use the CBTC moving block interlocking system to illustrate the synergy of the iStar and Z combination on complex software systems. Finally, we verify the developed formal model against LTL safety properties using the ProZ model checking tool.