The Need for Flexible Requirements in Dependable Systems

For many critical systems, in addition to satisfying functional requirements it is important also to address qualities such as performance, availability and safety, which are attributes of dependability. Engineering practice has shown that it is impossible to achieve all dependability requirements without compromise. The satisfaction of requirements depends on design decisions during system evolution and contextual information about the operation of the system. A key challenge is to maintain the multiple attributes of dependability at acceptable levels, addressing the achievement of each attribute in context of the others. This task requires definition and justification of clear levels of acceptability for each dependability requirement, as well as traceability of the requirements’ rationale throughout the entire lifecycle. Adopting a flexible approach when specifying satisfying requirements is a realistic and pragmatic approach, which lays the foundation for the evolution of requirements and the resolution of any conflicts that may appear.