Exposing the susceptibility of off-nominal behaviors in reactive system requirements

Requirements are typically specified on the assumption that the system´s operating environment will behave in what is considered to be an expected and nominal manner. When gathering requirements, one concern is whether the requirements are too incomplete to account for every possible, unintended, off-nominal behavior (ONB) that the operating environment can create in the system. In this paper, we present a semi-automated approach, based on the causal component model (CCM), which can expose, within a set of requirements, whether ONBs can result in undesired system states. We demonstrate how the CCM approach exposes and helps address potential off-nominal behavior problems in a set of requirements that represents a real-world product. Our case study shows that the approach can expose susceptibility to ONBs and can supply information in correcting requirements.