The good article at http://aviadezra.blogspot.com/2009/05/uml-association-aggregation-composition.html (found when trying to remember the meaning of UML association notations in http://en.wikipedia.org/wiki/File:Domain_model.png) discusses these, indicating the unique features of each:
Association - includes "weak" associations
Composition - denotes dependency (exclusivity)
There's a fourth, association that was not mentioned: Dependency (denoted by dashed arrow), which denotes weak association. Therefore, as far as I can tell, composition associations, in general, can be represented by either of Aggregation, Dependency, or Composition UML notation.
So, where is association notation useful? Many-to-many relationships and mutually navigable relationships.
More explanation on when to use arrows: http://awgquotes.blogspot.com/2012/02/uml-associations-objectmentor.html
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