The difference btw Association and Aggregation?

[peter king]

Hi Friend,

As teh topic says the difference between association and agregation? How to figure what to put out of those two?

Assume two class Applicant, Persona
1. Applicant has 1..M personas -- is this association or aggregation?

Thanks

[Geert Bellekens]

Peter,

As opposed to a Composition, there are no "hard" rules to decide whether or not an one-to-many association should be an aggregation. It is just a question of interpretation, and only has a functional meaning.
I see an an aggregation as a "whole" that groups the "parts" without owning them.
I wouldn't worry too much about the difference though.

Geert

[Oliver F.]

In fact an association is almost as generic as a dependency is.
Actors can be associated with use cases, components with interfaces, packages with classes, tables with tables, etc. It just means that element A has some intensive relationship with element B.

The aggregation is a referenced ownership relation meaning element A holds a reference to element B while the composition tells us B is directly included in A. Roughly spoken.

If we talk about how intensive a relationship between two elements can be (or the coupling) then the order would be:
The dependency is by far the weakest, followed by association,  aggregation and composition.

Oliver