Use Cases may have relationships with one another.

There are three standard types of relationships:

• Includes
  

   

  
  


• Extends
  

   

  
  


• Generalization
  

   

  
  

The includes relationship is used to prevent repetition of the steps required to other use cases. This shows the paths of functionality or the possible behaviours available to the user.

The extends relationship; extending use case may add behaviour to the base use case. The Extends relationship is used to show optional behaviour,which occurs under certain unusual conditions,and several different optional flows that may run based on Actor selection.

Use Case generalization is used when you want to document variation scenarios of particular use cases. A child use case will inherit behaviour of a parent use case.

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