Use Case

• Use Case is an integral part of requirements gathering.
• The requirements stage really has three parts: the Vision Document, Use Case Diagram, and Use Case Specification.  The Specification and Diagram usually go together.
• Take a look at the Argo users guide: http://argouml.tigris.org/documentation/defaulthtml/manual/ch03s02.html
• Read http://www.csc.calpoly.edu/~dbutler/tutorials/winter96/use/tutorial.html.
• The highlights:
• A use case captures the user's requirements, and maps them into a diagram understood by both end users and programmers.
• The use case shows the program as a black box - implementation details are not needed at this level.  That would be too confusing for the end user!
• Use cases have two requirements:
• Capture functional requirements.
• Structure the object model into a managable view.
• And, they have components
• Use case objects reside inside the system - they represent the black box program.  Use case objects can only interact with actors, not with other use cases.
• Actors are external to the system.  They have roles that define their interactions with the system.
• Lines connect use case objects and actors.
• To model a Use Case in Poseidon....
• Choose Create Diagram - Use Case
• You will find the actor, use case object, and line buttons on the menu bar.  Now you can just get to it!  (Example)
• Why are use cases important?  This all looks like a no-brainer, right?
• It is crucial to define system requirements ahead of time.  If not, you'll get in to scope creep, where users want more and will just assume that it is part of the system and current timeline.  With a use case, you agree early on.  If the user asks for additional features, you can then justify asking for more time (internal projects) or more money (consulting projects).
• A use case diagram example.

Created by:  Brandan Jones December 17, 2001