Links between objects are created and deleted over time. There are several approaches to modeling associations. We can
Create the objects and the link synchronously, and not build any statechart diagrams for the classes or the links.
Build a statechart diagram for one class or the other, endowing that class with the responsibility of managing creation and deletion of the objects and the link.
Build a statechart diagram for both classes, assigning the responsibilities for creating and deleting the link between the classes.
Abstract the association as an association class and use the association class to house the statechart diagram.
Some associations simply exist. ...