Uses Cases

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Uses Cases

• Keng Siau
• University of Nebraska-Lincoln

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Syntax for Use Case Diagram
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Actors

• An actor is someone or some thing that must
  interact with the system under development

Student
Registrar
Professor
Billing System
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Actors

• An actor represents a coherent set of roles that
  users of use cases play when interacting with the
  use cases
• Typically, an actor represents a role that a
  human, a hardware device, or even another system
  plays with a system

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Use Cases

• A use case is a pattern of behavior the system
  exhibits
• Each use case is a sequence of related
  transactions performed by an actor and the system
  in a dialogue
• It describes what a system does but NOT how it
  does it

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Use Cases

• A use case is a description of a set of sequences
  of actions, including variants, that a system
  performs to yield an observable result of value
  to an actor
• Each use case must have a name that distinguishes
  it from other use cases

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Use Cases

• Actors are examined to determine their needs
• Registrar -- maintain the curriculum
• Professor -- request roster
• Student -- maintain schedule

Maintain Schedule
Maintain Curriculum
Request Course Roster
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Use Case Diagram

• Use case diagrams are created to visualize the
  relationships between actors and use cases

Request Course Roster
Professor
Student
Maintain Schedule
Maintain Curriculum
Registrar
Billing System
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Use Case Relationships

• Can organize use cases by specifying
  relationships among them.
• Generalization
• Include
• Extend

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Use Case Relationships

• Generalization
• Child use case inherits the behavior and meaning
  of the parent use case
• Child use case may add to or override the
  behavior of its parent
• Child use case may be substituted any place the
  parent use case appears

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Use Case Relationships

• Include
• Base use case explicitly incorporates the
  behavior of another use case at a location
  specified in the base
• Use an include relationship to avoid describing
  the same flow of events several times
• by putting the common behavior in a use case of
  its own

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Use Case Relationships
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Use Case Relationships

• Extend
• An extend relationship between use cases means
  that the base use case implicitly incorporates
  the behavior of another use case at a location
  specified indirectly by the extending use case
• Use an extend relationship to model the part of a
  use case the user may see as optional system
  behavior

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Use Case Relationships
Included Use Case
Super Use Case
ltltincludegtgt
ltltextendgtgt
generalization
Extending Use Case
Sub Use Case