Use Case Diagrams Lecture Oo14 Use Cases

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

Teaching Points n What are Use Cases n Use Case Diagrams n Use Case Specifications

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

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

Use Cases n Every system function/requirement must stem from some user-visible function n 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).

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

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

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

Relationships Communication Associations n Also called “links” n Relates an actor to a use case it interacts with

Example:

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

Example:

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

Example:

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

Use Case Relationships

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: : Trader in association : Salesperson in association

Teaching Points n What are Use Cases n Use Case Diagrams n Use Case Specifications