Lecture – 7: Use Case Diagram
Interaction models
• Modeling user interaction is important as it helps to identify user
requirements.
• Modeling system-to-system interaction highlights the communication
problems that may arise.
• Modeling component interaction helps us understand if a proposed
system structure is likely to deliver the required system performance
and dependability.
• Use case diagrams and sequence diagrams may be used for interaction
modeling.
Use Case Modeling
• Use cases were developed originally to support requirements
elicitation and now incorporated into the UML.
• Each use case represents a discrete task that involves external
interaction with a system.
• Actors in a use case may be people or other systems.
• Represented diagrammatically to provide an overview of the use case
and in a more detailed textual form.
Use Case Diagrams
• Use Case diagrams show the various activities the users can perform
on the system.
– System is something that performs a function.
• They model the dynamic aspects of the system.
• Provides a user’s perspective of the system.
Use Case Diagrams
• A set of ACTORS : roles users can play in interacting with the system.
▫ An actor is used to represent something that uses our system.
• A set of USE CASES: each describes a possible kind of interaction
between an actor and the system.
▫ Uses cases are actions that a user takes on a system
• A number of RELATIONSHIPS between these entities (Actors and
Use Cases).
▫ Relationships are simply illustrated with a line connecting actors to
use cases.
Use Case Diagrams - Actors
• An actor is a user of the system playing a particular role.
• Actor is shown with a stick figure.
employer
employee
client
Use Case Diagrams – Use Cases
• Use case is a particular activity a user can do on the system.
• Is represented by an ellipse.
• Following are two use cases for a library system.
Borrow
Reserve
Use Case Diagram – Example1 (Library)
Library System
borrow
client
reserve
employee
Order title
Fine
payment
A Library System.
supervisor
Use Case Diagram for Student
Assessment Management System
Grade System
Record grades
Student
View grades
Teacher
Distribute
Report cards
Create report
cards
Printing administrator
system name
ATM System
primary actor
Bank
Customer
1
Withdraw
Money
association
use case
secondary actor
2
Deposit
Money
3
Transfer
Money
role
system boundary
4
Check
Balance
Customer
Accounts
Database
Use Case Diagrams - Relationships
• Inclusion
A base use case is dependent on the included use case(s); without
it/them the base use case is incomplete as the included use case(s)
represent sub-sequences of the interaction
• Extension
– Allows creating a new use case by adding steps to existing use
cases
• Generalization
– Allows child use cases to inherit behavior from parent use cases
Use Case – Example
(self service
machine – includes relationship)
<<includes>>
Open Machine
Restock
<<includes>>
Close Machine
<<includes>>
Open Machine
Collect
<<includes>>
Close Machine
Use Case – Example
(self service
machine – extends relationship)
<<includes>>
Open Machine
Restock
<<includes>>
<<extends>>
Restock According
to Sales
Close Machine
Use Case – Actor-to-Actor relationship
generalized actor
Cook
specialized
actor
Mom Cook
Father Cook
Use cases in the Mentcare system involving
the role ‘Medical Receptionist’
Include and Extend
Include:
• A base use case is dependent on the included use case(s); without
it/them the base use case is incomplete as the included use case(s)
represent sub-sequences of the interaction.
Extend:
• Extend is used when a use case conditionally adds steps to another
first class use case.
• The extending use case represents optional (should/could/want)
behavior. This is where the term optional is relevant
Include
Difference between Include and Extend
THE END