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TitleUML Distilled
TagsSoftware Development Conceptual Model Unified Modeling Language Systems Theory Object Management Group
File Size4.1 MB
Total Pages118
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Page 60


need to keep information about how awake that person was; we can do this by adding the attribute
attentiveness to the association.

Figure 5.12. Association class

Figure 5.13 shows another way to represent this information: Make Attendance a full class in its own
right. Note how the multiplicities have moved.

Figure 5.13. Promoting an association class to a full cl ass

What benefit do you gain with the association class to offset the extra notation you have to
remember? The association class adds an extra constraint, in that there can be only one instance of 
the association class between any two participating objects. I feel the need for another example.

Take a look at the two diagrams in Figure 5.14. These diagrams have much the same form.
However, we can imagine one Company playing different roles in the same Contract, but it's harder
to imagine a Person having multiple competencies in the same skill; indeed, you would probably
consider that an error.

Figure 5.14. Association class subtleties (Role should probably not be an
association class)

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