Use Case Diagrams

1. Use Case Diagrams Lecture Oo14 Use Cases

2. References • Booch, et al, The Unified modeling Language User’s Guide, AWL, 1999, Chapt 16 & 17 • Fowler & Scott, UML Distilled Applying the Standard Object Modeling Language, AWL, 1997, Chapt 3

3. Teaching Points • What are Use Cases • Use Case Diagrams • Use Case Specifications

4. Review • What are the phases of our S/W Eng method? • What happens in each phase? • What are analysis and design?

5. Use Cases • Use cases are an analysis tool • They describe typical interactions between a user and the system • Capture some user-visible function • Achieve a discrete goal for the user • May be small or large

6. Use Cases • Every system function/requirement must stem from some user-visible function • Take each discrete thing they want to do, give it a name, and write up a short textual description (no more than a few paragraphs).

7. Use Case Diagrams • Used for visualizing use cases and helping to understand system interactions with the various kinds of users. • Part of the UML notation

8. Actors • An actor is a role a user plays with respect to the system • There may be many persons playing the same role • One person can play more than one role • Actors carry out use cases • Actors don’t need to be human

9. Use Case • Capture some user-visible function • Achieve a discrete goal for the user • A specification is attached to each use case

10. RelationshipsCommunication Associations • Also called “links” • Relates an actor to a use case it interacts with

11. Example:

12. Useful for capturing exceptions Used for describing a variation in normal behavior The insertion of additional behaviour into a use case that does not know about it The Extend Relationship

13. Example:

14. The Include Relationship • Used when you have similar behavior across a number of use cases • In this case one use case uses another • Used when you are repeating yourself in two or more separate use cases and you want to avoid repetition • The insertion of additional behaviour into a use case that explicitly describes the insertion

15. Example:

16. Generalization Relationships • Used when you have one use case that is similar to another use case but does a bit more • The more specific use case inherits requirements from the more general use case and can add features to it

17. Use Case Relationships

18. Use Case Specifications Use Case name: Price Deal Category: Use Case View Documentation: This is some documentation for the Price Deal use case. You would provide one or two short paragraphs here. External Documents: Abstract: No State machine: No Generalization: Valuation (Uses) Associations: <no rolename> : Trader in association <no rolename> : Salesperson in association

19. Teaching Points • What are Use Cases • Use Case Diagrams • Use Case Specifications