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

The semantic of NonHierarchicalReferences is 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-hierarchical References, all concrete ReferenceTypes shall inherit from either hierarchical References or non-hierarchical References, either direct or indirect.

There are no constraints defined for this abstract ReferenceType.