A methodology for scenario-based requirements capture

Scenarios are an intuitive way for software project stakeholders to capture requirements, describe test cases and evaluate software architectures. Typically, however, coming up with a complete scenario specification is difficult. Basic (or nominal) scenarios are easy to write down, but more complex or less common (non-nominal) scenarios are harder to elicit. In particular, there is currently no good way of knowing when enough scenarios have been developed and scenario writing should stop. What is needed is a methodology for developing a scenario specification from an initial set of nominal scenarios, accompanied by metrics for deciding when the specification is complete. We sketch out a preliminary form of such a methodology in this paper.