What are Use Cases. Use cases are techniques to capture the func3onal requirements of a system

Transcription

1 What are Use Cases Use cases are techniques to capture the func3onal requirements of a system Describe the typical interac3ons between the users and the system, providing a narra3ve of how a system is used Expressing the problem that is understandable by skakeholders: users, developers, Can be used by the following ac3vi3es easily without much transla3on

2 Actor and Use Cases Use case: a sequence of ac3ons a system performs that yields an observable result of value to a par3cular actor Actor The user who interacts with the system Use case diagram

3 Use case diagram A system may have many use cases A system may have many actors A actor may perform many use cases

4 Content of Use Case No standard Informal, formal, high level, detailed level Start with the main success normal scenario Write as numbered steps Each step is an interac3on between an actor and the system Each step should be a simple statement and should clearly show who is carrying out the step The step show the intent of the actor, not the mechanics of what the actor does Do not describe the user interface the UI design will be derived from the user cases Then figure out all alterna3ve condi3ons For each step in the main scenario, ask what can go differently?

5 Use Case Template Name: Iden*fier (A unique iden)fier for this use case, e.g. UC10) Precondi*ons (List the state(s) the system can be in before this use case starts) 1. Basic Course (Describe the normal processing path, aka, the Happy Path) 1. Use case begins when Use case ends when Alternate Course A: Descrip*on of the alternate course Condi*on: Indicate what happened 1. List the steps Post condi*ons (List the state(s) the system can be in when this use case ends) 1. Source:

6 Good Use Cases Text No GUI No data formats 3-9 steps in main scenario Easy to read At user s goal level A record of decisions made

7 Use Cases aren t UML use case diagrams Describing the GUI Describing data formats Mul3ple- page main scenario Complicated to read At program- feature level A Tutorial on the domain

8 Good Example System: Course Enrollment System Use case: Register for Courses 1. Student requests to construct a schedule. 2. The system prepares a blank schedule form. 3. The system gets available courses from the Course Catalog System. 4. Student selects up to 4 primary course offerings and 2 alternate course offerings from the available offerings. 5. For each course, the system verifies that the Student has the necessary prerequisites, adds the Student to the course, marking Student as enrolled for that course in the schedule. 6. When the Student indicates the schedule is complete, the system saves the schedule.

9 Good example (cont.) Extensions: 2a. Student already has a schedule: System brings up the current version of the Student s schedule for edi3ng instead of crea3ng a new one. 2b. Current semester is closed and next semester is not yet open: System lets Student look at exis3ng schedules, but not create new ones. 3a. Course Catalog System does not respond: The system no3fies the Student and terminates the use case. 5a. Course full or Student has not fulfilled all prerequisites: System disables selec3on of that course and no3fies the Student.

10 Bad Example Register for courses 1. Display a blank schedule. 2. Display a list of all classes in the following way: The le` window lists all the courses in the system in alphabe3cal order. The lower window displays the 3mes the highlighted course is available. The third window shows all the courses currently in the schedule. 3. Do 4. Student clicks on a course. 5. Update the lower window to show the 3mes the course is available. 6. Student clicks on a course 3me and then clicks on the Add Course buaon. 7. Check if the Student has the necessary prerequisites and that the course offering is open. 8. If the course is open and the Student has the necessary prerequisites, add the Student to the course. Display the updated schedule showing the new course. If no, put up a message, You are missing the prerequisites. Choose another course. 9. Mark the course offering as enrolled in the schedule. 10. End do when the Student clicks on Save Schedule. 11. Save the schedule and return to the main selec3on screen. Source: hap://alistair.cockburn.us