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link
subject			fact

link	connects two objects - an instance of each of the two classes involved in the association
	has definition A reference from one object to another
	is a subtopic of 5.3 - Associations and Multiplicity
	is an instance of association
	is drawn as a line connecting two objects in a UML instance diagram
	is a kind of data abstraction
	never has multiplicity symbols
data abstraction	groups the pieces of data that describe some entity, so that programmers can manipulate that data as a unit
	helps a programmer to cope with the complexity of data
	hides the details of data
association	describes a relationship that will exist between instances at run time
	has default name "has" if it has neither an association name nor a role name
	has example class Person in a business application might have the following relationships supervisor (association to class Manager) and tasksToDo (association to class Task)
	has part association name
	has part role name
	is bi-directional unless it has an arrow at one end indicating directionality
	is legitimate only if its links will survive beyond the execution of any particular operation
	is usually implemented using instance variables in Java: you divide each two-way association into two one-way associations - so each associated class has an instance variable
	may be implemented in several ways in Java
	must not be added to a model unless it is relevant to the application - it will be needed to implement some requirement
	normally represents something that will be stored in a database
	represents all the links between two classes that may ever exist
	should exist if a class possesses, controls, is connected to, is related to, is a part of, has as parts, is a member of, or has as members, some class in your model
	shows how two classes are related to each other

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