Association   An association is a semantic or structural relationship between classifiers. An association has a name and consists of at least two association ends. The association ends are simply the end parts of the association where they connect to classifiers. It is the association's ends that may have a number of adornments that express the rich structural semantics of the relationship.

Explanation

This form of the association is one of the most common relationships in the UML. It is said to be binary, meaning that it is a relationship between two (and only two) classifiers. The association means that the two classifiers have a structural relationship, implying they are used together. Both of the classifiers that are connected by the relationship line have a perspective on the relationship. The point of connection between the line and the classifier signifies relationship. This is called the association end or the role that the classifier plays in the relationship. Most of the important properties of the association are expressed in the association end. The line itself is of little interest.

Important Points

		A binary association (connecting two classifiers) can only have an aggregate or composite at one of its two ends.		An association between two classifiers is said to be binary, meaning that, there are two classifiers taking part in the relationship. In this case only one of the ends can have the aggregation adornment of an aggregate (weak) or composite (strong) symbol. Note that with n-ary associations none of the association ends can be adorned with an aggregate or composite symbol.
		An association can be navigable in either one or both directions.		An association is said to be navigable, meaning that the association can be traversed from the end without the arrow to the end with the arrow.

Related Entries

Association Class  More General An association class is related to an association because its meaning is the same as an association but it adds the mechanism of the class to add features to the relationship itself. It is both an association and a class.

N-ary Association  More General An n-ary association is related to an association because it is a more general expression of the same concept. An n-ary association is a relationship between three or more classifiers, whereas an association is a relationship between two and only two classifiers. The "n" in n-ary refers to the fact that this more general association denotes a structural relationship between any number (n) of classifiers.