Simplifying Use Cases - Extend - Using an extend

6 important questions on Simplifying Use Cases - Extend - Using an extend

What is true about the Base Use case and the extension?

The Base Use Case goal can be met without also meeting the extension goal

In the book there is an "extreme example" of the extension.

Can you name an extreme example?

An extreme example is:

When the extension purpose is not related to the core goal.
Consider the behavior “Fill Out Survey” when attached to the “Borrow Book” Use Case.

The “Fill Out Survey” is not necessary to complete the “Borrow Book” goal, even though we might attach them together, with the “Fill Out Survey” as an extension.

Can you name an example of a extension of a deliver/release situation supporting new functionality in the  "" Hail a Ride" app?

Consider the Use Case “Hail a Ride.”

It may be a later version that allows the car to be reserved for a future time, “Reserve a Car.”

This “Reserve a Car” would be an extension of the normal path of “Hail a Ride.”
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What is an other common use of extension that is not entirely legitimate, but you can see this in the UML literature?

Another common use of extensions is to capture behavior that is optional at run-time.

I do not believe that this is indeed legitimate if the extension is still required occasionally to meet the Base, however, you will see this in the UML literature

Can you give an example of a behavior that is optional at run-time in the Library system?

Consider the Use Case, “Return Book”: occasionally it will also be necessary to “Pay Fine.”

Many modelers would make “Pay Fine” an extension, though I would make it an Included Use Case because I believe it is needed to meet the goal of “Return Book.”

If you feel that Pay Fine is not required to implement Return Book, then make it an extension.

This distinction is tricky and it is probably not worth the time spent in arguing about this on a project.

It often winds up being a big source of contention that is not that significant

When you model an extension Use Case, you have the ability to.... ?

specify the conditions (if any) that the extension behavior is run under

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