USE Case

1. Use Case Modeling

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Commonly Used UML Diagrams
The most commonly used UML diagrams are:
– Use case diagram, describing how the system is
used.
• The starting point for UML modeling.
– Use case (not a diagram).
– Activity diagram.
• Each use case may create one activity diagram.

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Commonly Used UML Diagrams
The most commonly used UML diagrams
(continued):
– Sequence diagram, showing the sequence of
activities and class relationships.
• Each use case may create one or more sequence
diagrams.
• A collaboration diagram is an alternative to a sequence
diagram.

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Commonly Used UML Diagrams
The most commonly used UML diagrams
(continued):
– Class diagram, showing classes and relationships.
• Sequence diagrams and CRC cards are used to
determine classes.
– Statechart diagram.
• Each class may create a statechart diagram, useful for
determining class methods.

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Overview of UML Diagrams

6. Use Cases
• Depiction of a system’s behavior or
functionality under various conditions as the
system responds to requests from users
• Full functioning for a specific business purpose

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Use Case Diagram
• A use (yoos) case describes what the system does,
not how it does the work.
• The use case model reflects the view of the system of
the user outside of the system.
• Symbols are:
– Actor, a stick figure.
– Use case, an oval.
– Connecting lines.

8. UML Use Case Diagram Symbols
Use Case
Actor
Boundary
Connection
Include relationship
Extend relationship
<<include>>
<<extend>>

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Actors
• Represent role played by one or more users
• Exist outside of the system
• May be a person, another system, a device, such as a
keyboard or Web connection
• Can initiate an instance of a use case
• May interact with one or more use cases and a use
case may involve one or more actors

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Actors (Continued)
• Actors may be divided into two groups:
• Primary actors supply data or receive
information from the system
• Secondary actors help to keep the system
running or provide help
– Help desk, analysts, programmers, etc.

11. What is a Boundary?
• A boundary is the dividing line between the
system and its environment.
• Use cases are within the boundary.
• Actors are outside of the boundary.

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Use Case
• Consists of three things:
– An actor (user) that initiates an event.
– An event that triggers a use case.
– The use case that performs the actions triggered
by the event.

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Use Case (Continued)
• Better to create fewer use cases
• 20 use cases for a large system
• 50 use cases would be the maximum for a
large system
• Can nest use cases, if needed

14. What is a Connection?
• A connection is an association between an
actor and a use case.
• Depicts a usage relationship
• Connection does not indicate data flow

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Use Case Relationships
• Communicates
– Connect an actor to a use case
• Includes
– Use case contains a behavior that is common to
more than one use case.
– The common use case is included in other use
cases.
– Dotted arrow points toward common use case.

16. What is an <<include>> Relationship?
• A connection between two use cases
• Indicates a use case that is used (invoked) by
another use case
• Links to general purpose functions, used by
many other use cases

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Use Case Relationships (Continued)
• Extends
– A different use case handles variations or
exceptions from the basic use case.
– Arrow goes from extended to basic use case.
• Generalizes
– One thing is more general than another thing.
– Arrow points to the general thing.

18. What is an <<extend>> Relationship?
• A connection between two use cases
• Extends a use case by adding new behavior or
actions
• Specialized use case extends the general use
case

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Use Case Relationships

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Steps for Creating a
Use Case Model
The steps required to create a use case model
are:
– Review the business specifications and identify
the actors within the problem domain.
– Identify the high-level events and develop the
primary use cases that describe the events and
how actors initiate them.

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Steps for Creating a
Use Case Model
• The steps required to create a use case model
are (continued):
– Review each primary use case to determine
possible variations of flow through the use case.
– Develop the use case documents for all primary
use cases and all important use case scenarios.