NB: For the purpose of this question, alternate scenarios are scenarios that aside from the main scenario also lead to the completion of the user goal; exceptional scenario are scenarios that do not lead to the completion of the user goal.
I've been having a conversation with my professor regarding one of his statements in class. He claims that "extend" should be used to model use cases that derives from exceptional scenarios. As an example:
(UC1: Publish blog post) ^ \ \-- <<extend>> -- (UC2: Error, empty blog post)
At this point given the definition of use case:
A use case is a set of scenarios (sequences of steps) that aim at accomplishing a end-goal for an user (actor).
I'm a little confused. If the error is a use case, what end-goal is it aiming at accomplishing? Does a user access the system to see the error message as an end-goal?
I've also went ahead and read about "extend" on the internet and I can't seem to find an example where the extension use case is an actual use case according to that definition. For example here we are given:
(UC1: Deposit funds) ^ \ \-- <<extend>> -- (UC2: Calculate bonus)
Again, what user end-goal is "Calculate bonus" trying to achieve? It almost seems as by definition, something that is only triggered by another case in certain situations cannot be considered a "use case" because it's not an end-goal.
Where am I wrong?