Applicability of SIGNAL in safety critical system development

The paper concerns the specification of functional and safety requirements of a safety critical system independently, and subsequent validation of the integrated requirements in the synchronous data flow formalism SIGNAL. The SIGNAL language provides a unified framework for hierarchical development of systems by refinement of specifications. Validation of specifications can be realised through a formal calculus based on the semantics of the language or through functional simulation. In this context, the research reported attempts safety management in critical real time systems in an application-independent manner. This is based on the possibility of identifying low and high risk states in a system and expressing its functional behaviour as transitions between pairs of states of different levels of risk. Safety requirements become conditions prohibiting low to high risk transitions, or forcing high to low risk transitions in a timely manner. A safety module, which is in charge of ensuring that these conditions are observed at run-time, is developed in SIGNAL to explore the applicability of the SIGNAL language to safety-critical design and to establish both the feasibility and the extent of managing safety concerns in an application-independent manner