6.14. Guideline: Take an Actor and Actor-Goal Perspective
Here's the RUP use case definition, from the use case founder Ivar Jacobson:
A set of use-case instances, where each instance is a sequence of actions a system performs that yields an observable result of value to a particular actor .
The phrase "an observable result of value to a particular actor" is a subtle but important concept that Jacobson considers critical, because it stresses two attitudes during requirements analysis:
- Write requirements focusing on the users or actors of a system, asking about their goals and typical situations.
- Focus on understanding what the actor considers a valuable result.
Perhaps it seems obvious to stress providing observable user value and focusing on users' typical goals, but the software industry is littered with failed projects that did not deliver what people really needed. The old feature and function list approach to capturing requirements can contribute to that negative outcome because it did not encourage asking who is using the product, and what provides value.92