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Use Case Modeling

Use Case Modeling. Use Cases are one way to capture requirements. A visual way to capture functional requirements Each bubble is a discrete user goal Actors can be people, or external systems Each bubble is mapped to a textual description. Use Case Description.

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Use Case Modeling

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  1. Use Case Modeling

  2. Use Cases are one way to capture requirements • A visual way to capture functional requirements • Each bubble is a discrete user goal • Actors can be people, or external systems • Each bubble is mapped to a textual description

  3. Use Case Description • See example on class schedule • Include basic and alternate/exception flows • Each alternate flow must start at a step in the basic flow, and may return to a step in the basic flow • Exception flows are analogous to exceptions in code • Includes versus preconditions • Do not use language that hints at implementation details or system interactions • Avoid click, press, type, button, etc. • Unnecessarily limits creativity

  4. Use Case Diagrams • Made up of three components • Actors (people or external systems) • Use Cases (with textual descriptions) • Relationships Record class grades Review Transcripts Teacher Student Authorized Staff Worker

  5. First, identify actors • Who or what will provide input to the system? • Who or what will need output from the system? • Exercise: identify three actors for an ATM

  6. Relationships between actors • One can be a specialization of another • Actors are classes, not individual people Student Graduate Student

  7. Next, identify user goals • User Goals are statements that represent what the users need to accomplish, independent of specific software features • “Buy a book” • “Return a book” • “View order history” • “Record a log for a transaction” • Exercise: identify five uses cases for an ATM https://commons.wikimedia.org/wiki/File:Girl_blowing_bubbles.jpg

  8. Finally, add relationships • Three types of relationships for use cases: Includes Extends Generalization

  9. Includes relationship • One use case can invoke the behavior of another • Not always, but often a precursor • I.e. the “Buy a book” use case includes the “Authenticate customer” Alter Student Grade <<includes>> Record Grades for a Section Teacher

  10. Extends Relationship • Similar to the includes, but used for handling an abnormal situation Alter Student Grade <<extends>> Alter student grade for a class taken more than a year ago Authorized Staff Worker

  11. Generalization Relationship • Replaces generic functionality with an alternate implementation Alter Student Grade Alter Student Grade for a Graduate Course Teacher

  12. Why Use Cases? • Visual representation easy to understand • Relationships are opportunities for reuse • Exercise: add one of each of the three types of relationships to your ATM example • Use case descriptions can be basis for testing • Can be the basis for planning and scheduling

  13. In-class Exercise • Examine the Quiz Game description • In your teams, come up with at least seven use cases; • At least three actors • At least one of each type of relationship • Complete a use case description for each use case • Turn in this assignment through XP-Dev • See instructions, rubric, and details on project page

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