UML class diagram

- the user must register (create an account)
- he can connect or disconnect
- he can take one or more quizzes
- he can add one or more events to his calendar
- he can write one or more messages on the forum

- the moderator can ask to add a quiz or event to the administrator
- the admin gives permission to the moderator
- the administrator can also add a quiz or event to the calendar
- the administrator can delete a user account, an event or a quiz