1. Use Cases & Use Case Diagrams
Chapter 3

2. Outline Use Case – defined Techniques for Identifying Use Cases
User Goal
Event Decomposition
UML's Use Case Diagram

3. Use Case - Defined Use case - an activity that the system performs
usually in response to a request by a user
Functional Requirements
Verb + Noun
Place order
Issue complaint
Techniques to Identify use cases:
User Goal
Event Decomposition

4. Identifying Use Cases- User Goal Technique
Ask the users what they need the system to do
Identify the users
Interview them
Create the list of use cases
Some users may need the same use case
Watch out for duplicates, inconsistencies
Verify the list with the users

5. Identifying Use Cases- Event Decomposition
Identify the events that occur to which the system must respond.
Event - an occurrence at a specific time & place which needs to be remembered
Use Case - what the system does when the event occurs
Prior Conditions & Events

6. Identifying Use Cases- Event Decomposition
Types of Events
External
Temporal
State

7. UML's Use Case Diagram

8. UML - The Unified Modeling Language
An Object-Oriented modeling language
"3 Amigos" - Booch, Rumbaugh, and Jacobson
Adopted & now managed by OMG (Object Management Group)
Models both structure & behavior
Structure diagrams
Class diagram, Component diagram, Deployment diagram, Object diagram, Package diagram, etc.
Behavior diagrams
Activity diagram , Use Case diagram , Sequence diagram, State machine, Communication diagram, etc. 8

9. <<system>>
Use Case Diagram
A UML diagram depicting the relationship between actors & use cases
Defines Scope/Functional Requirements
Symbols
Automation Boundary - The boundary between the software and the actors of the system
Actor - Anyone or thing that interacts with the system
Use Case - an activity that the system performs
Association - depicts a usage relationship between an actor and a use case
<<includes>> association - Used when one use case (base) includes another use case (the inclusion use case)
<<includes>>
<<extends>>
Time
Customer
Billing
<<system>>
<<uses>>

10. Use Case Diagram - Example
Prefer "Place an order"

11. Use Case Diagram - Practice
ATM System
Withdraw
cash
Customer

12. Use Case Diagram - Example
Create new order
<<includes>>
<<includes>>
Lookup
item availability
Customer
Validate
customer account
Sales
clerk
<<includes>>
<<includes>>
Update order
Reuse!

13. "Withdraw Cash” Use Case – i.e. scenario
Customer
Customer
ATM
Bank

14. <<Time>>
Special Use Cases
State-driven use cases
e.g. Polling, Monitoring, Notifications
Time-based Use Cases
Reorder
Stock
Employee
Generate
Payroll
<<Time>>