uml/class-diagram.md

@@ -20,4 +20,4 @@ The following figure shows an example UML class diagram, which reflects the requ
 ![Class Diagram](https://git.informatik.uni-kiel.de/ag-se/teaching-public/wikis/uml-sources/img/class-diagram.svg)
 
 ### Explanation
-We model several classes in order to represent the central objects within our web application *StudentData*.
+We model the most important classes in order to represent the central objects within our web application *StudentData*. We identify **five** classes, which are essential within our scenario (Student, Lecturer, Administrator, Lecture, and Exam). As the first three classes represent some kind of role within our software system, we model an abstract parent class **Person**, which contains attributes and methods, which every role needs and therefore inherits. An administrator manages student accounts and creates Lectures. A Lecturer can give Lectures and conducts Exams (at a specific date), alone or in collaboration with a second Lecturer, which he can perform via his same-named method. Students get examined and receive a grade for this exam. Each Exam is assigned to a single student, there is no grade for a student group or anything similar. The most interesting part within our diagram is the relation / association between Student and Lecture. If we take a look on the cardinalities, we see that a Lecture needs at least **five** students to be held. (as represented by 5..\*), but a Student can visit as many Lectures he likes (0..\*).