Use Case Diagrams
Use Case
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Use case
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A view to system seen from outside(user)
User’s requirements on system
A set of scenario for an actor to achieve useful
works
Withdraw
Transfer
Balance
check
Bank client
deposit
Bank system
Basic Concepts
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Actor
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User Case
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Each describes a possible interaction between an actor and the system
Use cases are actions that a user takes on a system
System
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An external person, process or thing interacting with a system or class
The entity that we are going to build
Can have subsystems in it
Relationship
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Connection between actors and use cases or use cases and use cases.
Actors
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A user of the system
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a person or another system
Identify the actors in terms of their roles
Use Case
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actions users take on system

can be very high level or so fine-grained
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Use “verb” or “verb+noun” style naming
borrow
return
System
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module that performs the function

System or the sybsystem is shown as a rectangle
enclosing the use cases, with the system name in the
rectangle
Library System
Relationship (Use Case Diagram)
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There are four kinds of relationships
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Association
Extend
Include
generalization
Association Relationship
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Shown by a line connecting actors to use cases
Include Relationship
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Between a use case and another use case
use case A includes the function of use case B
(has-a relationship)
A
<<include>>
B
Extend Relationship
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Use case can be extended by another use case
At the extension point, use case is extended
Extension point
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Shows the exact extension point between the two use cases
Shows the actual logic necessary for one use case to extend another
Example : Extend Relationship
Generalization Relationship
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Indicate an inheritance of an item in UML
Can be applied to actors as well as use cases
Example
Activity Diagram
What is Activity Diagram
•
Shows overall flow of control (just like
flowchart)
•
A simplified look at what happens during a
process
•
Business and operational step-by-step
workflows of components in a system
Activity Diagram Notations
Decision
Wake Up
Activity1
[hungry]
Wake Up
[Not hungry]
[hungry]
Activity2
Eat Breakfast
Go Back to Sleep
Eat Breakfast
Transition from
one activity to another
[Not hungry]
Go Back to Sleep
Two ways of showing a decision
Concurrent Path , Signal
Synchronization bar
Television
Remote.keyln(channel)
Work Out
Show New Channel
Change(channel)
Shower
Press Channel
Number
Change (channel)
Relax
Watch
Concurrent Path
Signal : when received, the signal
causes an activity to take place
(send : convex , receive : concave )
Swimlanes
• show who has responsibility for each activity. (role)
1. A salesperson calls the client and sets up an appointment
2. Onsite appointment(In the consulting firm’s office)
- corporate technicians prepare a conference room for a
presentation
3. Offsite appointment(at the client’s office)
- a consultant prepares a presentation on a laptop
4. The consultant and the salesperson meet with the client at
the agreed-upon location and time
5. the salesperson follows up with a letter
6. If the meeting has resulted in a statement of a problem, the
benefit – the activities of each role are clarified
9
Activity Diagram Example
Call client and
set up appointment
[appointment onsite]
[appointment offsite]
Prepare a conference
room
Prepare a
laptop
Meet with the client
Send followup
letter
See the
Activity Diagram
for Creating a
Document
[no statement problem]
[statement of problem]
Create proposal
Send proposal to client
1
Swimlane : shows “who” for each activity
Sales Person
Consultant
Corporate Technician
Call client and
set up appointment
[appointment onsite]
[appointment offsite]
Prepare a
laptop
Prepare a conference
room
Meet with the client
Send followup
letter
[statement of problem]
Create proposal
[no statement problem]
Send proposal to client
See the
Activity Diagram
for Creating a
Document
Example
Sequence Diagram
Purpose of Sequence Diagram
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shows the sequence of messages for a particular task from a
use case diagram
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Understand how use case(scenario) can be refined with detailed
information
Sequence Diagram
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Time, object, and message
 Lifeline and activation
Notation
:Name
Basics
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Focus on order in which messages occur
time
objects
:Name1 object
message
activation
lifeline
:Name2
Messages
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The first message starts at the top, typically located
on the left side
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Subsequent messages are then added to the diagram
slightly lower then the previous message
: synchronous call operation : method on the arrow
: asynchronous signal
: return message (optional) : return value on the arrow
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Messages can be sent to itself
Sequence diagram example
Object
Time constraint
Message
Activation
Comment
Example
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Sequence for “withdraw-money” use case