Derived Elements - UML

A derived element can be determined from others. Attributes and associations are the most common derived elements. When should derived elements be shown?

Guideline : Avoid showing derived elements in a diagram, since they add complexity without new information. However, add a derived element when it is prominent in the terminology, and excluding it impairs comprehension.

For example, a Sale total can be derived from SalesLineltem and ProductDescriptions information. In the UML, it is shown with a "/" preceding the element name.

Figure 31.22 Derived attribute

As another example, a SalesLineltem quantity is actually derivable from the number of instances of Items associated with the line item.

Figure 31.23 Derived attribute related to multiplicity

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