The HasSubtype ReferenceTypeis a concrete ReferenceTypethat can be used directly. It is a subtype of the HasChild ReferenceType.

The semantic of this ReferenceTypeis to express a subtype relationship of types. It is used to span the ReferenceTypehierarchy, whose semantic is specified in; a DataTypehierarchy is specified in 5.8.3, and other subtype hierarchies are specified in Clause 6.

The SourceNodeof Referencesof this type shall be an ObjectType, a VariableType, a DataTypeor a ReferenceTypeand the TargetNodeshall be of the same NodeClassas the SourceNode. Each ReferenceTypeshall be the TargetNodeof at most one Referenceof type HasSubtype.