Consider the course registration system at School of Management $($SoM$),$ University of San Francisco. Each department offers one or more courses and assigns only one of its instructors to teach each course. Each course is offered by only one department. The system shows the course number, name, and meeting time for each course, and the department number and name for each department. Each student can register for one or more courses, and at least one student is registered for each course. Also, each professor can teach one or more courses and works for only one department at SoM. However, if a professor is on the sabbatical leave, he$/$she will not teach any courses. For students, the registration system keeps track of the student$$s ID$,$ first name, last name, and email address, and for professors, the system keeps track of the professor$$s ID$,$ first name, last name, office location, and phone number.