It's from an imaginary application that models university courses. Each Course object maintains a list of the students on that course and the lecturer who has been assigned to teach that course The Course object has behavior that allow the adding and removing of students from the course, assigning a teacher, getting a list of the currently assigned students, and the currently assigned teacher. Teachers are modeled as Lecturer objects. As a lecturer may teach more than one course there is an association between Course and Lecturer. The "taughtBy" relationship shows that a Course only has a single teacher, but that a lecturer may teach several Courses. Each Lecturer object also maintains a list of the Courses that it teaches. There is a similar relationship between Course and Student. A course is attended by zero or more Students, and a Student may attend multiple courses. The diagram shows a Person interface that stipulates that objects conforming to this interface will have a getName and getEmailAddress methods. Both Lecturer and Student are shown to be types of Person.