UML Use-Case diagram questions

Question

I have a few questions regarding use-case diagram:

• If my system has register/login use-case for guest, should it be enabled for admin, user (i just wanna clarify, if i have login system, do i assume that admin, user etc. are people who already logged in to system so i skip them with logging thing)?

• If my system has a student actor, that is signing for individual seminars/courses, do i have (or am i allowed) to make use-case for ,,taking class'' after singing for them, and should there be relations between those 2

• Should my teacher inherit from student actor, since he can browse courses as well? (and so on admin?)

• Is my payment setup correct?

Answer 1

1. Remember that these are roles not people. An admin can be a guest, so long as they behave entirely like a guess, no special functions or rules. However, during log-in the user role could change, become admin. Note you are in some sense missing authenticate user, each use-case that requires security should include it, generally not extend.
2. Only if it interacts with the system, example, triggers an auto completion or is tracked in some way there of. Relations are not needed generally, associations could help communicate something that is ambiguous, but I am not sure what the would be in this case.
3. Nope, really then the role is any user could browse courses once they are authenticated. You could have students, admins, and teachers be sub-types of authenticated or associated person, etc.
4. Depends. Firstly you never pay and sign-up at the same time, so from a user standpoint that is broken. There are other ways in UML to connect this constraint of paying for courses. Process diagram, state diagram, etc. Because payment is really a long running transaction which can be hard to pin down. I would personally show the student and the external payment system interacting with the "payment" use cases.

Remember unless you are generating code most of the time UML is about communication so knowing your audience. Do not be afraid to use comments or constraints, if this is homework, use a constraint and get some real points. Maybe even put a constraint on the sign and pay course use cases.

Answer 2

1. If you want the admin to be able to log-in then he would have a use case for that. I agree that he most likely won't be registering, so maybe you want to break the register/log-in into two use cases?
2. You do not have to make a "Take Class" use case. Only make it, if that's how the user will interact with the system. My guess is that he won't be "taking" the class with the system, in which case it won't be a use case of the system.
3. I would think that you wouldn't want to inherit from student. First of all, from a realistic stand-point, it doesn't make sense. That would mean a teacher is-a student. You could extract that behavior to another parent class, but that might make the hierarchy too large and confusing.
4. If you are asking whether it is correct to say "sign for course" includes "pay for course," then maybe, it's probably better to use extend.

Another suggestion. The black arrow (usually means "dependency" in UML) you have between Actors and Use Cases, should probably be bi-directional, non-arrowed, line (this is usually called "association") At least that is what the UML standard says.