5.4: Use Case Diagrams
Use case and sequence diagrams are two key OO modeling diagrams for identifying and communicating requirements. This section explains and illustrates them by creating examples for the Post system.
The use case is the first key OO modeling diagram discussed for application in the requirements phase of the SDLC. Use cases are a powerful way of modeling what the system needs to do. "Actors" are key in capturing requirements; the following section elaborates on their use in requirements analysis.
This section goes into more detail on use case diagrams for requirements. What components are in a use case diagram (actors, extensions, stereotypes, and notes)? How are different interactions and features depicted for people who use the application? How are these features mapped into a use case diagram? Remember that a use case diagram cares about "what", not "how". This discussion provides a "big picture" of use cases, their use, and their relationship with "white box" details. These essential elements comprise a use case, rules-of-thumb guidance, the importance of the narrative text connected to a use case diagram, and user stories as an alternative to a use case diagram.