Aggregation is a whole/part relationship. This relationship denotes that the aggregate class (the class with the diamond touching it) is in some way the “whole”, and the other class in the relationship is somehow “part” of that whole.

There is not likely to be much difference in the way that the two relationships, Aggregation or Association, are implemented. That is, it would be very difficult to look at the code and determine whether a particular relationship ought to be aggregation or association. For this reason, it is pretty safe to ignore the aggregation relationship altogether. As the amigos said in the UML 0.8 document: “...if you don’t understand don’t use it.”

class Window

{

public:

//...

private:

vector<Shape*> itsShapes;

};

Strong form of Aggregation is Composition (black diamond).