Use Case Diagram for Stack Overflow

Question

I am trying to design a Use Case Diagram for an app like Stack Overflow. I have tried to add some basic functionalities in this diagram.

I want to improve this diagram to include an exhaustive list of all the features of Stack Overflow, but have no idea of how to do so. Also, should there be another actor for Admin who manages user accounts, or not? And if we are asked for Use Cases, should we describe the inner functionalities, preconditions and postconditions of each use case separately?

What if other than these two actors, I decide to add a Mediator actor too, who forwards the problems to the mentor, and when a mentor solves it, it is the responsibility of mediator to mark it solved?

Answer 1

If you want to map all the use cases and actors in StackOverflow you can take the Tour and search for some known Q&A in the Help Center.

And yes, if you want to make an exhaustive list, then you should include every actor - including Admin and Mediator. However, I'm not sure that you can figure out the admin's use cases (or other managing roles in this platform) since you are a user and it isn't reflected to you.

If there are use-cases that are unique to a specific actor, then you should add that actor to the diagram - and use inheritance! (When actor b has all the cases of a plus more, then b is inherits a) - this one is called "Generalization of an Actor" (you can google search some examples).

As for your other questions:

Please note that Use Case Diagram is an addition to the Use Case Modeling, more like an appendix. When you are modeling - you explain lots of details about the use case (some of them you've mentioned), such as: Primary actor, Scope, User Story, Postconditions, Preconditions, Triggers, Flow, and many more... There are a lot of templates actually. You can review them Here.

You do not describe visually* any preconditions or post-conditions, however, you have some tools that can describe which cases are **included in a specific case (in order to use feature Y - you should go over feature X). Or, which cases extends other cases (while you are using feature X, you can (but not have to) use feature Y).

Hope it helped :)

Answer 2

I encourage you to use a modeler rather than to draw your diagram by hand.

I want to improve this diagram to include an exhaustive list of all the features of Stack Overflow

The exhaustive list of the features of S.O. is certainly very be long, and you will have problem too see it because surely some parts are hidden to 'standard' users. What is your goal, to model S.O. or to use it as an exercise ? On the second case it is not necessary to manage all

should there be another actor for Admin who manages user accounts, or not?

Sure they are admins or 'super' users.

if we are asked for Use Cases, should we describe the inner functionalities, preconditions and postconditions of each use case separately?

A use case is not only an ellipse in a diagram, and a model is not ajust a list of diagrams. Yes each UC must have its description and the possible pre/post conditions etc

What if other than these two actors, I decide to add a Mediator actor too ...

I don't know if there are mediators, but I am quite surprised by the 'mentor' whose role is to answer. If you have him you make a separation between the roles consisting to ask and to answer, so the other role cannot be the very general user but probably must be more specific

You will have lot of remarks about the UC login for sure ;-)