How to use extend and include use cases in UML?
Include : An include relationship defines that a use case contains behaviors defined in another use case. In other words, the base case explicitly incorporates the behavior of another use case at a location specified in the base use case.
Extend: A relationship from an extending use case to an extended use case that specifies how and when the behavior defined in the extending use case can be inserted into the behavior defined in the extended use case. In other words, the extending use case adds itself to the extended use case. Most of the time, an extend relationship has a condition attached to it. The extending use case executes only when the condition is true.
Include vs Extend Use Cases
Include Use Case - The include use case never stand alone. When an actor initiates any base use case then base use case executes included use case.
Extend Use Case - The extending use case may stand alone, but under certain conditions, its behavior may be extended by behavior of another use case.
References
Use Case Driven Approach for Agile Development
