Exceptional use cases

Many exceptional situations arise during the execution of an application. When developing dependable software, the first step is to foresee these exceptional situations and document how the system should deal with them. This paper outlines an approach that extends use case based requirements elicitation with ideas from the exception handling world. After defining the actors and the goals they pursue when interacting with the system, our approach leads a developer to systematically investigate all possible exceptional situations that the system may be exposed to: exceptional situations arising in the environment that change user goals and system-related exceptional situations that threaten to fail user goals. Means are defined for detecting the occurrence of all exceptional situations, and the exceptional interaction between the actors and the system necessary to recover from such situations is described in handler use cases. To conclude the requirements phase, an extended UML use case diagram summarizes the standard use cases, exceptions, handlers and their relationships.