Unified Medical Language System (UMLS)

Unified Medical Language System (UMLS) is a comprehensive list of biomedical terms for developing computer systems capable of understanding the specialized vocabulary used in biomedicine and health care.  

The Unified Medical Language System  was developed by the National Library of Medicine (NLM). NLM produces and distributes the UMLS Knowledge Source databases and associated software tools for use by system developers in building or enhancing electronic information systems that create, process, retrieve, integrate, and/or aggregate biomedical and health data and informatics research. All UMLS Knowledge Sources and associated software tools are free of charge to U.S. and international users.

The UMLS consists of these major components:

Metathesaurus: This serves as the core database for the UMLS.  It is the raw collections of concepts and terms from various controlled vocabularies and their relationships. The Metathesaurus has a license agreement because it includes vocabulary content produced by different copyright holders as well as content produced by NLM.

Semantic Network: These are the overall categories that the information from the Metathesaurus is divided into, as a method of organization.

Specialist Lexicon: This is a database of lexicographic information for use in natural language processing.  This database holds the criteria for the categorization of the concepts in the Metathesaurus.  The Specialist Lexicons define the categories of the Semantic Network, which is the organizer for the individual terms and concepts in the Metathesarus.

In addition to access to SNOMED CT  within the UMLS Metathesaurus, UMLS licensees also have free access to SNOMED CT in its native file formats, to the documentation of these files and to a set of subsets and mapping files.  UMLS licensees have broader rights to create and distribute SNOMED CT extensions and derivative works under the uniform international IHTSDO Affiliate License that is now part of the UMLS License. The license covers all types of use in all countries. Fees apply to some types of distribution or use in countries that are not yet Members of the International Health Terminology Standards Development Organization (IHTSDO).

This was last updated in July 2010

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