Use Cases

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Use Cases
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Overview

• Use cases are used primarily for requirements
  specification.
• They model specifically how different actors will
  use the system under analysis
• They are often created in several iterations
  starting with the most general statements, then
  decomposing them into more and more specific
  cases.

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Symbols
An actor is someone or something that interacts
with your system, that uses it. It is normally a
type like customer rather than a particular
person or thing
A use case is an oval that describes a use, or
requirement of the system. It always begins with
a verb, and can be numbered.
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Actor and Use Case
A line shows that an actor uses a particular use
case
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Uses Relation
The uses relation says that one or more use cases
use another. It has implications in terms of
later programming, implying that both can rely on
a single module or class
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Extends Relation
The extends relation models possible inheritance
in terms of generalization/specialization. Here
the Create Report is the general use case and the
two types of reports are specialized cases.
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System Boundary
One can use a system boundary box to show the
limits of the system under consideration
Not part of the system
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Decomposition
Individual use cases can be decomposed into
more specific use cases. (Note the numbering)
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Description

• In addition each use case can be described
  verbally, there are many ways to do this.
• Often the text identifies the use case,
  identifies the triggerthe event that causes
  the use case to be used, and the steps involved
  in the use case.
• The next slide has an example

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Example

• Use Case 1.1 Enter New Project
• Primary Actor Project Worker
• Trigger project worker begins new project
• Use Case Steps
• Worker Opens main form
• Selects new Project
• 3. Enters Project title, start date, estimated
  duration, other relevant information
• 4. Worker saves new project to database
• 5. Worker exits or chooses to begin a task on new
  or previous project