===== Definitions and Terms =====
For purposes of the OMOP Common Data Model (CDM), the following terms are used:
^Term^Description^
|Standardized Vocabularies|Contains a system of Vocabularies, Classifications, Domains and Concepts all consolidated into a common format and stored in a set of CDM tables.|
|Vocabulary|A set of codes or concepts, including if available relationships amongst them, including if available a hierarchy, ontology or taxonomy of the concepts. Many vocabularies are adopted from national or international organizations, such as ICD-9-CM, SNOMED-CT, RxNorm, Read.|
|Terminology|Similar to vocabulary and often used synonymously, but not used in this document.|
|Coding scheme|Similar to vocabulary and often used synonymously, but not used in this document.|
|Classification|A hierarchical system of concepts and concept relationships that defines semantically useful classes, like chemical structures for drugs.|
|Domain|A clinical semantic category, like Drug, Condition, Procedure defined for all Concepts in the Standardized Vocabularies.|
|Concept|Basic unit of information defined in each Vocabulary.|
|Concept Class|An attribute of a concept characterizing it's classification within a Vocabulary. The difference to the Classification is that a Concept Class is a single attribute without any hierarchical structure.|

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