Use Case Diagrams

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Use Case Diagrams

• Lecture Oo14
• Use Cases

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References

• Booch, et al, The Unified modeling Language
  Users Guide, AWL, 1999, Chapt 16 17
• Fowler Scott, UML Distilled Applying the
  Standard Object Modeling Language, AWL, 1997,
  Chapt 3

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Teaching Points

• What are Use Cases
• Use Case Diagrams
• Use Case Specifications

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Review

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

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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

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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).

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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

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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 dont need to be human

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Use Case

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

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RelationshipsCommunication Associations

• Also called links
• Relates an actor to a use case it interacts with

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Example
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The Extend Relationship

• 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

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Example
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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

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Example
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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

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Use Case Relationships
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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
ltno rolenamegt Trader in association
ltno rolenamegt Salesperson in
association
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Teaching Points

• What are Use Cases
• Use Case Diagrams
• Use Case Specifications