Engineering Safety Requirements, Safety Constraints, and Safety-Critical Requirements

As software-intensive systems become more pervasive, more and more safety-critical systems are being developed. In this column, I will use the concept of a quality model to define safety as a quality factor. Thus, safety (like security and survivability) is a kind of defensibility, which is a kind of dependability, which is a kind of quality. Next, I discuss the structure of quality requirements and show how safety requirements can be engineered based on safety's numerous quality subfactors. Then, I define and discuss safety constraints (i.e., mandated safeguards) and safety-critical requirements (i.e., functional, data, and interface requirements that can cause accidents if not implemented correctly). Finally, I pose a set of questions regarding the engineering of these three kinds of safety-related requirements for future research and experience to answer.