Use Cases Week 8 CMIS570
Refresher – Class Diagrams Appointment scheduling example Car Rental example E-Commerce example
UML diagrams • 9 diagrams • Used throughout SDLC • Use consistent syntax and notation. • Key building block is the use-case.
Use-Case • Requires you to break system into use cases, small logical pieces of the system and deal with each separately. • In contrast, DFDs and ERDs encompass the entire system in one diagram.
Use-Case Diagrams • Graphical specification of the system’s behavior from the perspective of the user(s). • Describes what the system does without describing how the system does it. • They are used to identify and communicate the high-level business requirements for the system.
Use-Case contains: • Actor • Event/Use Case • Association • System boundary
Example! • Patient Admission system
Example • Car Rental System
Another example • E-commerce system
Steps in creating a Use-Case • 1. Identify use-cases (find major functions) • 2. Draw the system boundary • 3. Place use-cases on the diagram (6-8 use-cases per diagram) • 4. Identify the actors • 5. Add associations
In addition… • Text documents to document use-cases since use-case diagram does not describe how those use cases are carried out by the actors. • When describing the use-case, you should focus on its external behavior – how it interacts with the actors, rather than how the use case is performed inside the system.
Steps in Documentation • 1. Create a use case template that has areas labeled Basic Course and Alternative Courses. • 2. Ask “What happens?” • 3. Ask “And then what happens?” • 4. Ask, “What else can happen?
Documentation examples • Patient Admission • Rent a car • Search by Author
TIPS • Think usage scenario rather than functional requirements. • Describe usage rather than attributes and methods. • Don’t write use-case too tersely. • Don’t ignore system responses. • Don’t forget alternative courses of action
Includes statement • When one use-case needs to use another use-case • Two types • Internal – only other use-cases reference • Both external actors and internal use-cases reference
Examples • Order Entry • Class registration