One of your goals during analysis is to identify potential opportunities for reuse, a goal you can work toward as you are developing your use-case model. Potential reuse can be model through four generalization relationships supported by UML use-case models:

• Extend dependencies between use cases

• Include dependencies between use cases

• Inheritance between use cases

• Inheritance between actors

For more detail, you can read the following aritcle.

http://www.agilemodeling.com/essays/useCaseReuse.htm

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