The Association relationship models a relationship between objects that is not covered by another, more specific relationship.
Used to model relationships between Business Objects or Data Objects that are not modelled by the standard relationships.
The Association relationship is also used to link the informational concepts with the other concepts: a Business Object with a Representation, a Representation with a Meaning, and a Business Service with a Purpose.
The Association relationship can be used when drawing a first high-level model where relationships are initially denoted in a generic way, and later refined to show more specific relationship types.
Structural.
Some Business Objects and a Business Contract are all associated with each other.