Urban railway interlocking system is a safety-critical system, for which interlocking rules are well-defined by international standards to assure safe operations. However, it is very difficult to extract all of the safety requirements in the requirements engineering stage itself and construct a goal model as well. One approach to fulfill this goal is to extract safety requirements from regulations and analyze them at the early stage of the model. Improper specifications regarding the environs

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... an interlocking system are realized to be accountable for any faults in requirements specifications. Furthermore, nonfunctional requirements are kept aside from requirements specifications. To make an interlocking system operate in an ultra-dependable range we need to address variability issues, so in this paper, we used i*-based goal-oriented requirements language called TGRL to address variability issues as well as blend early and late requirements. The developed model can also be visualized and analyzed using jUCMNav. Finally, the safety requirements to be verified are specified with Formal Tropos, a formal specification language for the i* model.