In our work with acquisition programs, we've often observed a major problem: requirements specifications that are incomplete, with many functional requirements missing. Whereas requirements specifications typically specify normal system behavior, they are often woefully incomplete when it comes to off-nominal behavior, which deals with abnormal events and situations the system must detect and how the system must react when it detects that these events have occurred or situations exist. Thus, although requirements typically specify how the system must behave under normal conditions, they often do not adequately specify how the system must behave if it cannot or should not behave as normally expected. This blog post examines requirements engineering for off-nominal behavior.
Background: In our research and acquisition work on commercial and Department of Defense (DoD) programs, we see many systems with critical safety and security ramifications. With such systems, safety and security engineering are used to managing the risks of accidents and attacks. Safety and security requirements should therefore be engineered to ensure that residual safety and security risks will be acceptable to system stakeholders. The first post in this series explored problems with quality requirements in general and safety and security requirements in particular. The second post, took a deeper dive into key obstacles that acquisition and development organizations encounter concerning safety- and security-related requirements. This post introduces a collaborative method for engineering these requirements that overcomes the obstacles identified in earlier posts.
Background: In our research and acquisition work on commercial and Department of Defense (DoD) programs, ranging from relatively simple two-tier data-processing applications to large-scale multi-tier weapons systems, one of the primary problems that we see repeatedly is that acquisitionand development organizations encounter the following three obstacles concerning safety- and security-related requirements: