Simple Classifiers – DataTypes
Figure 40 shows an extract from the DataTypes diagram from the UML specification. It defines the two non-abstract metaclasses DataType and PrimitiveType. These data types differ from classes in the sense that there is no object identity for their instances. Instances of data types are only differentiated from one another based on their value. Simple data types (PrimitiveTypes metaclass) have no internal structure.
Figure 41: Class diagram with two primitive data types