Multiplicity Relationship in Class Diagram
First of all, let’s start with the meaning of multiplicity. Multiplicity is a relationship between two related classes refers to the other. For instance; a mother has kids; kids have a mother.
First one is Association relationship (knows, users). Association relationship is a link between two related things. I am going to give an example from your presentation; you said there are a person and one individual property. If there is no person or no property, it cannot be a relationship. I think association relationship is the validity of multiplicity.
The second one is Aggregation by value and Aggregation by reference relationships (is part of, consist of). Aggregation by value means the lifetimes of the objects are the same, the person was born, and he has a head. If the person doesn’t have a head, he cannot live. Aggregation by reference, the whole may not have a part, or it may have a different part at a different time. I will give an example again from your presentation, the guy wants to go hiking, but his hiking club is going to announce bankruptcy. Then the guy is going to look for another hiking club. When we look at both relationships, they are not the validity of multiplicity. In aggregation, by value’s example, the human and the head doesn’t refer each other, because the human and the head are the lifetimes of the objects are the same. In aggregation, by reference’s example, the guy is hiking, and hiking club is going to announce bankruptcy, these don’t make reference each other too. If the club is closed, the guy can find another hiking club.
The third one is Generalization/Specialization relationships (is kind of). What kind of car do you like? Sports car. The sports car is the type of vehicle. The sports car is a class; the vehicle is another class. They are related, but they don’t reference each other. There are too many different types of cars. It can be any other type of cars instead of a sports car. Therefore generalization/specialization relationships are not the validity of multiplicity.
The last one is Dependency relationship that one class depends on another because it uses it at some point in time. For example electricity class and lamp class, lamb depends on electricity and but electricity doesn’t depend on the lamb. Therefore dependency relationship is not the validity of multiplicity.