DREP: A Requirements Engineering Process for Dependable Reactive Systems

Discovering and documenting potential abnormal situations and irregular user behavior that can interrupt normal system interaction is of tremendous importance in the context of dependable systems development. Exceptions that are not identified during requirements elicitation might eventually lead to an incomplete system specification during analysis, and ultimately to an implementation that lacks certain functionality, or even behaves in an unreliable way. This paper presents a requirements engineering process, DREP, that systematically guides the developer to consider reliability and safety concerns of reactive systems. After the discovery of normal system behavior by means of use cases, the developer is lead to explore exceptional situations arising in the environment that change the context in which the system operates and service-related exceptional situations that threaten to fail user goals. The process requires the developer to specify means that detect such situations, and to define the recovery measures that attempt to put the system in a reliable and safe state. The process is iterative, and refinements are carried out, if necessary, to achieve desired quality levels. To conclude the requirements phase, an extended use case diagram summarizes the normal interactions, exceptions, handlers and their relationships. The proposed process is demonstrated with the 407 Express Toll Route System case study.