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navigability for the end that should not be referenced. Figure 5.6 shows how to
make your selection.
Setting an end to be not navigable adds an arrow to the opposite end—so that it
appears as a one-way path between the elements. The end without an arrowhead is not navigable (cannot be referenced by the other end). Figure 5.8 illustrates the both types of end points.
Figure 5.8
Association End: Arrowhead used for Navigability
FridgeSimulation is not
navigable (known about) by
FridgeModel
FridgeModel is navigable
(known about) by
FridgeSimulation
In this example of navigability, the FridgeSimulation can refer to the FridgeModel, but
the FridgeModel knows nothing about the FridgeSimulation.
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5-8
Multiplicity Association ends can also show multiplicity, which indicates the
number of objects of one class that are associated with an object in another class.
For example, you can specify that a refrigerator has two doors, or that a thermostat is associated with x number of temperature sensors. You can choose not to
specify multiplicity at all, signifying either that it is unimportant or it is undetermined. To specify a value, right-click the association and follow the steps in
Figure 5.9. The various ways of specifying multiplicity are described below.
•
Any number (including zero) Use an asterisk (“*”) to show that you can
have any number of class or interface objects associated with that association end.
•
A specific number Enter an exact number of class or interface objects
associated with that association end. For example, you can specify that
your refrigerator has two doors by entering “2” for the association end
near the Doors class.