Qualified Associations
A qualified association is the UML equivalent of a programming concept variously known as associative arrays, maps, and dictionaries.
Figure 6-13. Qualified Association
Figure 6-13 shows a way of representing the association between the Order and Order Line classes that uses a qualifier. The qualifier says that in connection with an Order, there may be one Order Line for each instance of Product.
Conceptually, this example indicates that you cannot have two Order Lines within an Order for the same Product. From a specification perspective, this qualified association would imply an interface along the lines of
class ...
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