4. Adding Associations and Navigability
In a design class diagram, associations are chosen by
a Spartan software-oriented, need-to-know criterion
i.e. what associations are required to satisfy visibility
needs indicated by the interaction diagrams.
This is in contrast with associations in the conceptual
model, which may be justified by the intention to
enhance comprehension of the problem domain.
Here are common situations suggesting a need to
define an association:
A sends a message to B.
A creates an instance B.
A needs to maintain a connection to B.