The NonHierarchicalReferences ReferenceTypeis an abstract ReferenceType; only subtypes of it can be used.

The semantic of NonHierarchicalReferencesis to denote that its subtypes do not span a hierarchy and should not be followed when trying to present a hierarchy. To distinguish hierarchical and non-hierarchicalReferences, all concrete ReferenceTypesshall inherit from either hierarchical Referencesor non-hierarchical References, either direct or indirect.

There are no constraints defined for this abstract ReferenceType.