如何建模（UML、类图）在方法中使用的对象

Question

I'm working on a class diagram for an existing application (C#) and I'm struggling with the following.

Say you have two classes A and B . Class B contains a method foo that returns a list of A objects::

public class A { string V {get; set;} }

public class B { 
    string W {get; set;} 

    public List<A> foo(JObject bar) { /* do something */ }
}

What is the relationship that A has with B in this case when this is modelled in UML?

At first I thought this would be a one-to-many relationship where the method returns a list (one or more...) of A . Because when you have a list attribute in a class, it is usually a one-to-many relationship. However, I don't know if this is the same case.

In the application, the A class is only used through the method foo() , so it would also be weird to connect it to nothing, as it would then just be a standalone class which I think is wrong too.

Answer 1

The only thing that we can say for sure is that B uses A : B needs to know about A since it returns a list thereof.

This kind of relationship is called a dependency : more precisely, it is a «use» dependency . A dependency has no multiplicity: there is no difference if the B uses several times A or only once; the dependency just means that it has to know about A .

If you would have a one-to-many association between B and A , it would mean that a structural relation: at a moment in time an instance of B could be linked with some instances of A s. Returning one or several A is not sufficient to create a link, because each A created and returned may be disconned from the B and as soon as the A's would be returned, B could not find them back either. No link, no association. The association would require something more durable, comparable to a property .