Generalizations
A generalization represents an inheritance relationship between a general class and a more specific class. The more specific class is fully consistent with the more general class and inherits its characteristics and behavior. However, it also contains additional information. Any instance of the more specific class is also an instance of the general class.The concept of generalization was initially used for classes, but has been extended to other UML concepts such as actor and use case.
Examples of generalizations between actors:
The "Client" actor can have the USA or Export specialization.
To create a generalization between actors in a use case diagram:
Click the 
button and drag the link from the specialized actor (eg: USA client) to the more general actor (eg: Client).The generalization then appears in the drawing.
When creating a second generalization, a dialog box allows you to reuse the existing generalization if it involves the same subject.