What is Generalization Relationship in Use Case Diagram?
Generalization is used when you find that two or more use cases have behavior, structure, and purpose in common. When this happens, you can describe the shared parts in a new, usually abstract use case, which is then specialized by the child use cases.
A parent use case can be specialized into one or more child use cases, representing a more concrete form of the parent use case.
Neither the parent nor the children are necessarily abstract, although the parent is abstract in most cases.
The child use cases depend on the structure of the parent use case and the children inherit all the structure, behavior, and relationships of the parent.
All children of the same parent are specializations of the parent.
References
Use Case Driven Approach for Agile Development
