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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:
* Classification Concept (standard_concept = 'C'). These Concepts are not used to represent the data uniquely in the CDM data tables, but provide hierarchical classes where the Standard Concepts are members. For example, the MedDRA concept for “COPD” has hierarchical relationships to the Standard SNOMED-CT Concepts that are all forms of this disease. Classification Concepts are sourced from different Vocabularies. Note that Classification Concepts are not unique. For example, there are Concepts for the Drug Class “Anticoagulants” coming from the NDF-RT, VA Class, ETC and ATC Vocabularies. Also note that the membership depends on the Vocabulary. In most cases the membership list of equivalent Classification Concepts are similar or identical, but the Medical Science does not provide a generally agreed upon standard definition of these classes.
For all Concepts in a Domain, this creates the following logical structure: