Use cases

Definition: A use case captures a contract between stakeholders about the behavior of a program.

Who might be a stakeholder?

• Customer
• Developer
• Marketing
• Management
• Regulator
• Lawyer
• Anyone who has a vested interest in the system

The use case describes how a system behaves as follows:

• The primary actor makes a request of the system in order to achieve a goal
• The system responds, protecting the interests of all stakeholders
• Each different sequence of behavior that unfolds is a scenario

(Adapted from Writing Effective Use Cases, Alastair Cockburn)

Writing Use Cases:

1. List actors and goals
   • Decide what goals of which actors the system will support
   • Prioritize goals
2. Main success scenario
   • For each supported goal, write a short, dry account of how an actor interacting with a system achieves that goal
   • Review use case to ensure that it meets the interests of the stakeholders
3. Failure conditions
   • List all ways in which the system could fail
   • DO NOT figure out how to handle them yet; first, list them completely
4. Failure handling
   • Write how the system will respond to each failure condition