Features
Figure 35 shows an extract from the Features diagram, supplemented with content from the Properties diagram in the UML specification. At the center is the non-abstract metaclass Property with its base classes. Attributes of classes and association ends are based on the Property metaclass.
The Class diagram in Figure 36 shows four UML elements of the Property type: the Order number and Number attributes, and the order and itemline association ends. These diagrams actually also include the two Attribute association ends for the respective opposite class. This is dealt with in more detail in the section on the Association metaclass The association edge shows a black diamond at the opposite end of order. This means that the order items are part of the order and are existentially dependent on it, that is, deleting the order includes deleting its order items. This kind of association is known as a composition. At the order association end, the diamond is displayed if the Property::aggregation property of the itemline association end has the value AggregationKind::composite.