Use Cases Introduced by Ivar Jacobson in 1986 literal translation from Swedish ”usage case” - may be of use to you in the future “blackbox” style is recommended - specify what the system must do, and not how it must do it. A project may begin with the definition of many “brief” or “casual” use case definitions. Later on, these can be become “fully dressed”

Use Cases Widely used. Not just an OO technique. Each Use Case will meet one or more user goals Collectively, Use Cases represent the functionality required by a system. Stories of using a system to meet goals

Use Cases Ch 6. Use Case example is very lengthy and fairly complete must read: pages 45-61, and sections 6.12, 6.13, 6.15 Ch 25 shows ways of managing Use Cases. Ch 25. The Use Case has been broken down into multiple Use Cases that are related via > and > must read: sections 25.1, 25.2, 25.3, 25.5 Ch 13. Contracts Ch 9. System Sequence Diagrams SSDs show the events that actors generate. The system is a black box and so the diagram emphasizes the events the system must respond to.

Use Cases a Use Case is initiated by an Actor Describes functional requirements from the user’s perspective illustrate actors & tasks forms: pictorial (defined in UML) textual not defined in UML recommended to leave UI details out and focus on the purpose of the use case focus on what the system does, not how it does it (black box)

Use Cases numerous textual forms brief, casual, fully dressed single- vs two-column form common format at Risks/dangers when using use cases: too much focus on functionality may lead to non- OO system

Actors An actor is anyone or thing that interacts with the system. These people or things are at the boundaries of the system. Suppose our system interacts with a billing system: Instructor Student Assign duties Assign grades Register for courses Browse enrollments Chair Billing Its common to place non-human roles on the RHS

Use Case Diagram

An Order-Processing System Place order Get Order status Send catalog Cancel order Return product Deliver product Send us product Calculate postage Customer Customer Rep Shipping company Supplier Clerk