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 March 21, 2001 [posted]
 NLM's Unified Medical Language System® (UMLS®)

T he goal of the National Library of Medicine's Unified Medical Language System (UMLS) project is to facilitate the development of applications that connect users and relevant machine-readable biomedical information. The UMLS involves a combination of three Knowledge Sources (the Metathesaurus®, the Semantic Network, and the SPECIALIST Lexicon) plus a variety of lexical programs and a tool for producing custom subsets of the Metathesaurus. These interfaces make use of the Knowledge Sources to help users in different environments find machine-readable information relevant to their particular practice or research problems. Priorities for the UMLS project include developing applications that make use of the Knowledge Sources and using feedback from these applications to guide ongoing enhancement and expansion of the Knowledge Sources. Medical librarians are heavily involved in the direction of the UMLS project, in the development of the Knowledge Sources, and in their applications. The UMLS tools and Knowledge Sources are primarily designed for systems developers; these are not end-user applications. Using the UMLS may require significant computing resources and technical effort. NLM itself uses UMLS data and associated programs in a variety of applications including the PubMed Translation Table, HSTAT,, and the Visible Human, as well as research related to natural language processing and computer-assisted indexing.

Introducing New UMLS Site
From time to time, the NLM Technical Bulletin will include information about the UMLS, reporting on new developments and informing medical librarians and other readers about the UMLS. One such recent development is the introduction of NLM's new UMLS Web site at This public site provides a broad range of information on the UMLS that will be useful for both new and existing users.

What's on the New Web Site?
Many individuals have questions when they first encounter the UMLS. The new Web site is designed to answer these questions and provide tools for learning about and using the UMLS. The site currently contains links to several resources including a list of Frequently Asked Questions, UMLS Documentation, UMLS Learning Resources, UMLS Tools, Bonus Files, and much more. If these resources don't provide the answers, users may pose their question to the appropriate address under UMLS Contact Information or to other UMLS users via the UMLS Listserv.

This Web site contains information about the UMLS and its uses; it does not contain the actual contents of the UMLS. No license agreement is needed to access the information on this site. If you want access to the UMLS itself, you must sign a license agreement. Information about the license and related copyright information is available from the new informational Web site.

This site is part of NLM's continuous effort to ensure that medical librarians and other interested parties are provided with usable information in order to increase their skills and knowledge about medical informatics and the UMLS.

By Carolyn B. Tilley
MEDLARS Management Section

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Tilley CB. NLM's Unified Medical Language System (UMLS). NLM Tech Bull. 2001 Mar-Apr;(319):e3.


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Last updated: 11 April 2012