Scenario

A scenario, in architecture evaluation, is a brief narrative describing an expected or anticipated use of a system, written from the point of view of both its developers and its end users. Where the abstract notion of "quality" is difficult to reason about directly, a scenario makes it concrete and tangible by grounding it in a specific situation. Something happens to the system, and the system is expected to respond in a particular, measurable way.

A scenario is conventionally described using four parts: an event or stimulus – some condition or event arriving at the system; the system, or the part of it, that is stimulated by that event; the response – the activity the system undertakes once the stimulus arrives; and a response measure – a metric by which that response can be judged, so the scenario states not just what should happen but how well it should happen.

Scenarios are usually grouped into three kinds: usage scenarios (or application scenarios), which describe how the system is meant to be used in normal operation; change scenarios (or modification and growth scenarios), which describe how the system is expected to evolve; and failure scenarios (boundary, stress, or exploratory scenarios), which describe how the system should behave when something goes wrong.

Scenarios that describe a required quality attribute form the leaves of a quality tree, and are the concrete inputs to evaluation methods such as the Architecture Tradeoff Analysis Method (ATAM).

See also

• Use case

References

• Kazman, R, Abowd, G, Bass, L, and Clements, P (1996). Scenario-Based Analysis of Software Architecture. IEEE Software, 13(6), 47–55.