Link and Association are the means for establishing relationship among objects and classes.
Link and Association often appears as verbs in problem statement.
Link is physical / conceptual connection among objects most links relate two objects, but some links relate three or more object. It is am instance of association as shown in figure below.
Association is a description of a group of links with common structure and common semantics as in the class diagram shown in figure below.
Association are indirectly bidirectional.
Both the direction of traversal is equally meaningful.
It is the only name of the association that established the direction.
Developers often implements association in programming language as a references from one object to another.
Associations are important, precisely because they break encapsulation.
Association cannot be private to a class, because they go beyond classes.
