我如何表示用例的条件？

Question

I'm in the specification part of a project and i have to make use cases but i don't understand how to translate this scenario. The project is: Students and teachers have to check in with a card in every class and the system counts presences and absences, if the teacher doesn't check in it doesn't count any absences because it's like there was no class. When the student reaches 25% absences the system sends an email to the teacher and student warning them.

My question is should the act of "checking in" be the same use case if it has different repercussions for each actor? How do i represent that if the teacher didn't check in then there's no class?

Answer 1

A use case is not dynamic view of the system, like flow control. it's a list of use case, main fonctionnality with a goal. The only condition that may appear is about extension point for extend use case

Answer 2

A use case is a use case. It shows the added value it will deliver to its primary actor. There is nothing that changes a UC due to scenarios running the one or other way.

In order to show conditions you need to add constraints. There is no need to show them in a UC diagram since there might be too many and will just confuse readers. If at all you want to show constraints you place them in a note and put curly brackets around the text like { this is some constraint} . A better place for constraints (unless your UML tool offers something better) is a textual description of the UC containing a table of constraints (along with scenarios etc.). Use a template from Cockburn or something similar.