用例图中的参与者之间的关系

Question

I'm wondering is it a mistake or I don't understand it correctly. As I know we use arrows between actors to present generalization (Student <- Undergraduate student), but how to interpret it in those 2 cases? (Cause Graduated Student is not more specified Undergraduate Student)

Thank You in advance!

Answer 1

The arrow with the open head on the left side represents a Generalization in UML. The arrow on the right side is not UML.

Generalization can be read as is a . So in this case you can read Graduate Student is a Undergrad Student . Whether or not that statement is correct is another question.

Answer 2

The left Generalization between actors makes sense as it represents some kind of competence hierarchy. This is often done in the sense of "the specialized actor can do/takes part in UCs which the general one can do/is associated with".

In contrast the right Generalization does not make sense. Use cases represent the single pieces of individual added value a system has. Using generalization will lead this ad absurdum. In that case Submit Exam is the basic use case. You would add either a constraint or some explanation in the UC description to tell that it is also used for a Thesis but never create two different UCs. The goal in both cases is to achieve a higher grade. Just that a Thesis can be sent only by a Graduate (this is the constraint).