1. Use Cases
Yonglei Tao

2. Typical Commercial Applications
entries in model dictionary
use cases
5-20 activities per use case
domain classes
1 to 12 operations per class

3. Use Cases Use case-iteration allocation matrix Business goals & needs
Current situation
Accommodating
Requirements Change
Customer
feedback
Acquiring
Requirements
Iteration use cases
Domain Modeling
Preliminary requirements
Domain model
Domain model
Deriving Use Cases
from Requirements
Actor-System Interaction Modeling
Abstract & high level use cases, use case diagrams
Expanded use cases & UI design
Allocating Use Cases & Subsystems
to Iterations
Behavior Modeling &
Responsibility Assignment
Behavior models
Use case-iteration allocation matrix
Deriving Design Class
Diagram
Producing an Architecture Design
Design class diagram
Software architecture
Test Driven Development, Integration, & Deployment
(a) Planning Phase
(b) Iterative Phase – activities during each iteration

4. A Use Case Diagram Library System Patron Checkout Document
Return Document
Patron
Search for Document

5. Simplify with Use of Inheritance
Library System
Checkout a
Document
Patron
Return a
Startup
Shutdown
Admin

6. Simplify with Use of Inheritance
Login
Logout
SAMS/Search Program
SAMS
End User
Admin
Staff
This is OK.
Login
Logout
SAMS/Search Program
SAMS
End User
Admin
Staff
Better

7. Are These Use Cases? Why? Check authorization / check authentication
Enter a password
Process data
Open a file
Click on a menu item
Traverse a linked list.
Start a system

8. Use Case Diagram – Overly Complex
Log In
Log Out
Start Up
SAMS
End User
Staff User
Admin
Add Program
Delete Program
Edit Program
Create User
Delete User
Update User
Search for Programs
Display Program
Detail
Apply Online
Shutdown

9. SAMS/User Mgmt Add Program SAMS Delete Program Admin SAMS Staff
Edit Program
SAMS/Program Mgmt
SAMS
Staff
SAMS/User Mgmt
Create User
Delete User
SAMS
Admin
Update User
Start Up
Software engineering
principle applied:
separation of
concerns
divide and conquer
Shutdown
Search for Programs
Display Program
Detail
Apply Online
SAMS/End User
SAMS
End User
SAMS/Authentication
Login
Logout
SAMS
End User
SAMS
Admin
SAMS
Staff

10. Verify the Use Cases Identified
Ask questions about each use case:
(1) Is it a business process?
(2) Is it initiated by an actor?
(3) Does it end with the actor?
(4) Does it accomplish something useful for the actor?
All the answers to above questions must be “yes”

11. Example: Library System
Requirements of a library system:
R1. The library system must allow a patron to
check out documents.
R2. The library system must allow a patron to
return documents.
system
actor
use case
Use Case
Business Process?
Begin w/ Actor?
End w/ Actor?
Useful Task for Actor?
Use Case?
Actor
System
Checkout Document
Library System R1 Y Y Y Y Y
Patron R2
Return Document Y
Patron
Library System

12. Example: Oversea Exchange Program
R1. The web-based application must provide a search capability for overseas exchange programs using a variety of search criteria. R2. The web site must provide a hierarchical display of the search results to facilitate user navigation from a high level summary to details about an overseas exchange program.
System
Actor
Use Case?
Useful Task for Actor?
End w/ Actor?
Begin w/ Actor?
Business Process?
Use Case R1
Search for Programs Y
User
Web App. R2
Display Program Details

13. Requirements Use Case Tractability
Will the system satisfy all the requirements?
Are any use case missing?
Are any use case not needed?
Which requirements are more important than the other?
Which use cases should the developer focus on timely delivery?

14. Requirements-Use Case Traceability Matrix
UC1
UC2
UC3
UC4
UC5
UC6
PriorityWeight
Score 3 2 1 X 5

15. Project Planning by Use Cases
1) Identify dependencies between the use cases:
use cases are business processes
business processes depend on each other
2) Compute a partial order to develop the use cases according to the dependencies.
3) Schedule the development according to the partial order
begin with higher priority use cases (risky, high-value, architecturally significant, and executable)
time-boxed iterations

16. Project Planning with Use Cases1 2 3 4 5 6 7 8 9 10 11 12
UC1
UC2
UC3
UC4
UC5
UC6
UC7
UC29
UC30 X
...
A planning tool to let the development team know
which use cases to be developed by what time
which use cases are ready for integration and system testing
what is the status or configuration of the project

17. Actor-System Interaction Modeling
Specify how the system interacts with the actors to carry out the use cases.
to identify what is expected from the system
In an expanded use case

18. Expanded Use Case – Initiate a Call
Actor: Caller
System:
Telco
actor input &
actor action
1.the caller picks up
the handset from
the phone base.
system response
2. the system generates
a dial tone.
3. the caller dials each
digit of the phone
number.
4. the system responds
with a DTMF tone for
each digit dialed.
5. the caller finishes
dialing.
6. he system produces
the ring tone.
7. the caller hears
the ring tone.

19. Domain Model and Use Cases
Part of Domain Model
Program
name
type
department
institution
subject
region
country
language
term
Student
Staff
Application
student_name
year
date_applied
status
manage
1..* *
with
name, type, department, ...

20. Expanded Use Case – Add Program
Precondition: Staff User has logged into System and Staff Main Page is shown
Actor: Staff User
System: SAMS
0. System displays the staff main page.
1. TUCBW the staff user clicks the
“Add Program” button.
2. System displays the Add Program
page.
3. The staff user enters program detail and clicks the ”submit" button.
4. System checks the submitted info and shows a confirmation message if no error is found.
5. TUCEW the staff user clicks the
“OK” button on the confirmation
page.
Postcondition: The added program is immediately available for search.

21. Showing User Interface Prototypes
Showing user interface prototypes with expanded use case specification is extremely useful to obtain user feedback early in the lifecycle.
These user interface prototypes may be reused in the preparation of the user’s manual, which can take place concurrently with the development effort.

22. Showing UI Prototypes w/ Expanded Use Case
(7) TUCEW staff member is shown a message that the program has been successfully added.
(6) The System updates the database with the new program details and displays a success message.
(5) User fills the form and clicks on submit button.
(4) System shows the Add Program Form
(3) Staff member clicks on Add Program link.
(2) System shows the submenu consisting of various operations that a staff user can do under Program Management.
(1) TUCBW staff member clicks on Program Management link on welcome page.
System : SAMS
Actor : Staff User

23. Video Store Use Case Diagram

24. Banking System Use Case Diagram

25. Validate PIN Use Case

26. Withdraw Funds Use Case

27. Class Exercise
What are the use cases for the Vending Machine?

28. Class Exercise: The Vending Machine
The Vending Machine has a display, an alphanumeric keypad, a coin insertion slot, and an item dispenser. The display shows the vending items like chocolates, candies, potato chips, Coke, sprite, etc. Each type of item has a price and a label consisting of a letter A, B, C, ... and a digit 1, 2, ... A customer inserts coins through the coin slot. Each time a coin is inserted an LCD displays the total amount. The customer can press a letter and a digit to enter his selection after enough coins have been inserted. If the total amount is greater than or equals to the item selected, the vending machine dispenses the item and returns the change to the customer. A customer can change his mind and request that the coins be returned by pressing the return button.