Methodological Support for Formally Specifying Safety-Critical Software

Abstract

We present the concept of an agenda and apply this concept to the formal specification of software for safety-critical applications. An agenda describes a list of activities to solving a task in software engineering, and validations of the results of the activities. Agendas used to support the application of formal specification techniques provide detailed guidance for specifiers, schematic expressions of the used specification language that only need to be instantiated, and application independent validation criteria. We present an agenda for a frequently used design of safety-critical systems and illustrate its usage by an example. Using agendas to systematically develop formal specifications for safety-critical software contributes to system safety because, first, the specifications are developed in a standardized way, making them better comprehensible for other persons. Secondly, using a formal language yields specifications with an unambiguous semantics as the starting point of further design and implementation. Thirdly, the recommended validation criteria draw the specifier’s attention to common mistakes and thus enhance the quality of the resulting specification.