A subjective methodology for safety analysis of safety requirements specifications

This paper presents a methodology for subjective safety analysis of safety requirements specifications of software for safety-critical systems. The methodology incorporates fuzzy set modeling and evidential reasoning to assess the safety associated with safety requirements specifications. Three basic parameters-failure likelihood, consequence severity, and failure consequence probability are used to analyze a safety rule in terms of membership functions. The subjective safety description associated with the safety rule is then mapped back to the defined safety expressions which are also characterized in terms of membership functions. Such a mapping results in the production of the safety evaluation associated with the safety rule. The information produced for all safety rules can then be synthesised using an evidential reasoning approach to obtain the safety evaluation associated with the safety requirements specifications. The developed methodology is capable of dealing with multiple safety analysts who make judgements on each safety rule. A case study based on a train-set crossing is used to demonstrate the methodology.