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The Standardized Vocabularies are organized into Domains and Vocabularies. Domains refer to the nature of type of a clinical entity, which also defines the CDM data table where a data record is stored, while Vocabularies are sets of Concepts imported from external national or international existing standards, or created by the Standardized Vocabularies Team if no suitable standard is available.
There is no one-to-one relationship between Domains and Vocabularies. Some Vocabularies are very broad, such as SNOMED-CT or Read, and contain Concepts of all medical Domains. Other vocabularies are specific for a certain Domain, such as RxNorm for Drugs or ICD-9-Proc for Procedures. In many cases Vocabularies are generally assumed in the community to be of a single Domain, when in fact they are not: For example, CPT-4 and HCPCS, are expected by their name to contain Procedure codes, only, but contain Observation, Condition, Device and Drug Concepts:
Within a Domain, codes come from a number of Vocabularies, and their codes have often identical or overlapping meanings. To bring order to this situation, each of them is assigned one of three designations:
For all Concepts in a Domain, this creates the following logical structure:
Source Concepts are mapped through a mapping mechanism to Standard Concepts, and these have relationships of various semantic natures to each other. In addition, they have hierarchical relationships to each other and the Classification Concepts, in this case derived from the Vocabularies A, B and C. Hierarchical relationships amongst Classification Concepts generally are only happening between Concepts of the same Vocabulary. All Concepts are stored in the CONCEPT table, all relationships in the CONCEPT_RELATIONSHP table and all generation-spanning hierarchical relationships in the CONCEPT_ANCESTOR table. The latter are only defined between Standard and Classification Concepts, Source Concepts do not participate in this hierarchical tree structure.