Informal Use Case
Patron Loses a Book The library patron reports to the librarian that she has lost a book. The lost a book. The librarian librarian prints out the library record prints out the library record and asks patron to speak with the head librarian, who will arrange for the patron to pay a fee. The system will be updated to refl
Formal Use Case
1 GOAL Patron wishes to reserve a book using the online catalog 2 Primary Actor Patron 3 Scope Library system 4. Level User 5. Pre Conditions Patron is at the login screen 6. Success end Conditions Book is reserved 7. Failure End Conditions Book is not reserved 8. Triggers Patron logs into system 9. Main Success Scenario 1. Patron enters account and password Scenario
2. System verifies and logs patron in System verifies and logs patron in
3. System presents catalog with search screen
4. Patron enters book title
5. System finds match and presents location choices to patron
6. Patron selects location and reserves book
7. System confirms reservation and re-presents catalog
10. Extensions ( error scenarios) 2a. Password is incorrect (error scenarios)
2a.1 System returns patron to login screen
2a.2 Patron backs out or tries again
11. Variations Patron enters author or subject
Steps in creating a use case
1. Identify actors and their goals
What computers subsystems and people will drive our computers, subsystems and people will drive our system?
2. What does each actor need our system to do ?
3. Write the success scenario
– easiest to read and understand
– everything else is a complication on this
Capture each actor's intent and responsibility, from trigger to goal delivery
– say what information passes between them say what information passes between them
– number each line
4. List the failure extensions
5. List the variations
Use case description
1. How and when it begins and ends
2. The interactions between the use case and its actors, including including when the interaction interaction occurs and what is exchanged .
3. How and when the use case will need data from or store data to the system .
4. How and when concepts of the problem domain are handled