Defining new ReferenceTypesshould only be done if the predefined ReferenceTypesare not suitable. Whenever a new ReferenceTypeis defined, the most appropriate ReferenceTypeshould be used as its supertype.

It is expected that Serverswill have new defined hierarchical ReferenceTypesto expose different hierarchies, and new Nonhierarchical ReferenceTypesto expose relationships between Nodesin the AddressSpace.