Identifying Dissonance and Other Dangers from Requirements

There is an important interface between requirements and safety engineering, but its very existence causes a problem: it belongs to neither discipline. This paper looks at identifying failure modes from a requirements perspective, and considers how the two disciplines can most effectively collaborate. Requirements techniques have evolved rapidly in the last 10 years from the traditional hit-and-miss list of "shall" statements to a mix of approaches that can be applied systematically, including the analysis of goals and scenarios. Many of the failure modes hardest to identify derive from the increasingly wide range of functions carried out within systems, mostly by software. Fortunately, these functions are designed to satisfy requirements, often both discovered and organised using scenarios. Hence, scenario-directed search offers a powerful and systematic means of discovering functional failures. But `dissonance\´, failure caused by undesired interactions within systems, presents a deeper problem.