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umluse-caseuse-case-diagram

What's the difference between extension use case and parent use case?

I'm so confused about the difference between extension use case and parent use case in Use case diagram. I would like to know when can I use the extend and when can I use the parent use case?

For example :

  • Print Slip extend Confirm
  • pay through PayPal inherits Payment.
  • pay through credit card inherits Payment.

What's the difference between inherits and extend ?

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Image source : https://t4tutorials.com/use-case-diagrams/

Solution

  • All proportions kept to compare the extend and the include + generalizations is like to compare the aggregations a and b + generalizations in :

    enter image description here

    In your diagram because of the extend the behavior defined in the UC Print Slip can be inserted into the behavior defined by the UC Confirm Order

    The generalizations are like they are elsewhere in UML, pay through paypal is a Payment and pay through credit card is a Payment too. The diagram indicates the UC Confirm Order includes the UC Payment or one of the two inheriting UCs. So the behavior of the UC Confirm Order contains unconditionally the behavior of the UC Payment or the behavior of the UC pay through paypal or the behavior of the UC pay through credit card.

    There is an example of inheritance between UCs in the norm, see figure 18.11 page 646 in chapter 18.1.5 of formal/2017-12-05