A safety enhancement model of software system for railways

The objective of the work is to propose a safety enhancement model of software system with improved specifications for railways. The safety critical nature of such software system, forces the safety requirements to be specified correctly and completely in an unambiguous manner at the analysis stage itself. Since the railways system safety relies on the synchronization and collaboration between different software process modules, the overall system safety can be enhanced by declaring fine grained specifications and then formally verifying them. The safety software system may face some operational disturbances due to unpredictable variations in the assumed environment like climatic changes that have not been specified. These leads to hazards and the application developed based on the incomplete specifications that runs on the predetermined hardware have to adapt its behavior to minimize the risk. In the proposed model, enhanced safety specifications are arrived along with the hazards table and verified in VDM++.The criticality matrix is constructed for all the hazards in different design contexts of railway system based on which safety specifications are enhanced. A Safety Specification Quality Index (SSQI) metric is proposed to evaluate the safety enhancement.