Use Cases - PowerPoint PPT Presentation

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Use Cases

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Use Cases Elizabeth Bigelow CS 15-499C 9/15/2000 Administration Only 4 students have submitted applications for TogetherJ Accounts Please get these in no later than ... – PowerPoint PPT presentation

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Title: Use Cases


1
Use Cases
  • Elizabeth Bigelow
  • CS 15-499C
  • 9/15/2000

2
Administration
  • Only 4 students have submitted applications for
    TogetherJ Accounts
  • Please get these in no later than Sunday evening

3
Use Cases
  • A form of dynamic modeling
  • Very informal
  • Tend to be unwieldy for large systems
  • Not a bad way to start, but usually will not
    scale well
  • Easy for users to understand
  • Difficult to use for embedded systems

4
Use Case Contents
  • Use cases (ovals)
  • Actors
  • Dependency, generalization and association
    relationships

5
Common Uses
  • Model the context of a system
  • Draw a line around the whole system and assert
    which actors lie outside the system and interact
    with it. Use case diagrams specify the actors and
    the meaning of their roles
  • Model the requirements of a system
  • Specify what the system should do independent of
    how the system should do it (ie, desired behavior
    as a black-box)

6
Credit Card Validation System Context
7
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8
If you start from use cases
  • Decide who interacts with the system (may be an
    external system)these are the actors
  • Decide what lies within the system (the system
    boundary
  • Develop high level use cases, then use
    generalization, dependency and association to
    make more precise
  • Note that in this context association is the
    relationship of the actors and the use cases

9
More details on use cases
  • Extends relationship is used to show
  • Optional behavior
  • Behavior that is only run under certain
    conditions
  • Several different flows which may be run based on
    actor selection

10
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11
Scenarios
  • A scenario is a specific instance of a use case
  • Expressing the whole system via scenarios is
    tedious, and time consuming
  • Specifying a few scenarios, however, can
    significantly help getting started

12
80/20 Rule
  • For any technique, keep the 80/20 rule in mind
  • Dont specify everything!
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