About the RDA Registry and vocabularies
RDA Reference includes all RDA Elements, their definitions and any related scope notes, and all value vocabulary terms and definitions.
RDA Elements include entities, attributes, relationships, and relationship designators described in RDF. The value vocabularies include the controlled terminologies for RDA data given in the Toolkit instructions, and a controlled terminology used with the instructions in general. These are described as Simple Knowledge Organization System (SKOS) Concepts in RDF.