Sending Messages in UML

In this paper we try to clarify the issue of associations as a communication infrastructure between objects, in search for a unified view of the static and dynamic aspects of associations. Communication through associations depends on navigability and visibility, therefore the interlacement of these two concepts is examined. But first the very definition of navigability has to be settled, since the concept of navigability of associations in UML is poorly explained in the official documentation. The coherent representation of the sending of messages in different UML diagrams helps to better understand the underlying metamodel and shows that a link in a collaboration diagram is not always an instance of an association.