Use Cases

Intro

• Use cases can be used to capture the systems functional requirements.
• Defined the systems functional acceptance tests.
• A use case does two things:

1. Describe how an actor achieves a goal using the system. This is described in terms of scenarios.
2. Interests of stakeholder are protected by the system.

Actor

• An actor is someone or something external to the system and who interacts with the system.

Scenario

• A scenario is a description of a sequence of actions that is a way of achieving a goal.
• The main success scenario is the usual/main/straightforward way of achieving the goal.
• All scenarios have
  • A precondition : required condition before starting.
  • Interaction steps
  • Postcondition :
    • Guaranteed state of world once use case exits. successful precondition holds for successful exit.
  • A minimal postcondition: Something that guarantees to protect stakeholder interests.

• For each step of main success scenario, think of:
• Secondary Scenarios:
  • Alternative Scenario: A different way of achieving success (the goal)
  • Exception Scenario: Something that can go wrong - and can lead to a different postcondition.