Requirements Engineering for Hard Real-Time Systems: theΣNotation and a Case Study

Requirements engineering is generally acknowledged to be vital for every system development project, especially when the system to be developed has to meet hard real-time demands, usually while operating in a safety-critical environment. The $\Sigma$ (Sigma) Notation, which is a new way of specifying formal well-structured requirements, suitable for hard real-time systems, is presented in this paper. The main characteristics of the notation are: formal underpinning, modelling flexibility, understandability from both engineers and users, rigorous handling of traceability for the derivation of requirements, and an interface to subsequent object-oriented analysis. We also present an extended example of the $\Sigma$ Notation’s use by modelling the Generalized Railroad Crossing.