1. Faculty of Computer & Information
Use Case Diagram
Faculty of Computer & Information
Software Engineering
Third year

2. Use Case Diagram
A use case is a set of scenarios that describing an interaction between a user and a system. It displays the relationship among actors and use cases. 
The two main components of a use case diagram are use cases and actors

3. Use Case Diagram Use Case Actor
A use case describes a sequence of actions that provide
something of measurable value to an actor .
Actor
An actor is a person, organization, or external system that plays a role in one or more interactions with your system
A document describing the use case in details

4. Identifying Use Cases
Which functions does the actor require from system?
Does the actor need to read, create, destroy, modify, or store some kind of information in the system?
Does the actor have to be notified about events in the system

5. Identifying actors Useful questions
Who will use the main functionality of the system(primary actors)?
Who will need to maintain, administrate, and keep the system working (secondary actors)?
With which other systems does the system need to interact?
Who or what has an interest in the results (the value) that the system produces?

6. Use Case Examples

7. Use Case Examples

8. Creating Use Case Diagrams
Start by listing a sequence of steps a user might take in order to complete an action.  For example a user placing an order with a sales company might follow these steps. 
Browse catalog and select items.
Call sales representative.
Supply shipping information.
Supply payment information.
Receive conformation number from salesperson.

9. Creating Use Case Diagrams
Associations

10. Example
Students are enrolling in courses with the potential help of registrars.
Professors input the marks students earn on assignments
registrars authorize the distribution of transcripts (report cards) to students

11. University Information System
Input Marks
Enter in Course
Selected Courses
Student
Professor
Registrar

12. Structure of a Use Case Specification
Name
Actors
Trigger
Preconditions
Post conditions
Success Scenario
Alternatives flows

13. Triggers What starts the use-case? Examples: Customer reports a claim
Customer inserts card
System clock is 10:00

14. Preconditions
What the system needs to be true before running the use-case.
Examples
User account exists
User has enough money in her account
There is enough disk space

15. Post-Conditions A post-condition is the outcome of the use-case.
Examples
Money was transferred to the user account
User is logged in
The file is saved to the hard-disk

16. Success Scenario
The success scenario is the main story-line of the use-case
It is written under the assumption that everything is okay, no errors or problems occur, and it leads directly to the desired outcome of the use-case
It is composed of a sequence of action steps
Introduction | Diagrams | Writing | Linking | Guidelines

17. Success Scenario User enters product name, SKU and description
System validates product SKU
System adds the product to the DB and shows a confirmation message
Introduction | Diagrams | Writing | Linking | Guidelines

18. Success Scenario Example
User enters a keyword
System presents a set of search results, and sponsored products, all of which include name, short description and price
User selects a product
System displays a product page, including product information, reviews and related products
User adds the product to the shopping cart
Introduction | Diagrams | Writing | Linking | Guidelines

19. Reuse Opportunities
There are some types of relationships between use cases
Extends
Includes

20. Inclusion

21. Extension

22. How to make use case diagram
Make interviews with user or make site view.
From these interviews we can know actors and an overview of the use cases in the system.
Making more and more interviews allow you to know the details about use cases or another use cases

23. Example

24. Bank System
A bank has several automated teller machines (ATMs), which are geographically distributed and connected via a wide area network to a central server.
Each ATM machine has a
Card reader
Cash dispenser
keyboard/display
Receipt printer.
By using the ATM machine, a customer can
Withdraw cash from either a checking or savings account
Query the balance of an account
Transfer funds from one account to another.

25. Bank System
An ATM operator may start up and close down the ATM to replenish the ATM cash dispenser and for routine maintenance.
It is assumed that functionally to open and close accounts and to create, update, and delete customer and debit card records is provided by an existing system and is not part of this problem.

26. ATM: Use Case Model