Skip to Content
Archives
NLM Home | About the Archives

Skip NLM NavigationNLM Home PageFact Sheets Home Page
Contact NLMSite IndexSearch Our Web SiteNLM Home Page
Health InformationLibrary ServicesResearch ProgramsNew and NoteworthyGeneral Information

Fact Sheet
Unified Medical Language System®

Background:

In 1986, the National Library of Medicine (NLM), began a long term research and development project to build a Unified Medical Language System (UMLS ® ). The purpose of the UMLS is to aid the development of systems that help health professionals and researchers retrieve and integrate electronic biomedical information from a variety of sources and to make it easy for users to link disparate information systems, including computer-based patient records, bibliographic databases, factual databases, and expert systems. The UMLS project develops "Knowledge Sources" that can be used by a wide variety of applications programs to overcome retrieval problems caused by differences in terminology and the scattering of relevant information across many databases.

Development Strategy:

The project is directed by a multi-disciplinary team of NLM staff. NLM encourages broad use of the UMLS products by distributing quarterly editions free-of-charge under a license agreement. The Knowledge Sources are iteratively refined and expanded based on feedback from those applying each successive version.

UMLS Knowledge Sources:

There are three UMLS knowledge sources:
  • UMLS Metathesaurus ®
  • SPECIALIST Lexicon
  • UMLS Semantic Network

The Metathesaurus provides a uniform, integrated distribution format from over 100 biomedical vocabularies and classifications (the majority in English and some in multiple languages) and links many different names for the same concepts. The Lexicon contains syntactic information for many terms, component words, and English words, including verbs, that do not appear in the Metathesaurus. The Semantic Network contains information about the types or categories (e.g., "Disease or Syndrome," "Virus") to which all Metathesaurus concepts have been assigned and the permissible relationships among these types (e.g., "Virus" causes "Disease or Syndrome"). NLM also distributes associated lexical programs and software helpful in producing customized versions of the UMLS Metathesaurus. Annual editions of the Metathesaurus have been distributed since 1990.

There have been significant additions and changes to the UMLS Metathesaurus and the SPECIALIST lexicon which should improve their usefulness for many applications. For example, the normalization process used by norm has been changed to allow multiple normalized forms when an input form could be an inflection of more than one base form. This scheme allows a more linguistically motivated uninflection algorithm.

The "MetamorphoSys" software has been improved and is useful in producing customized versions of the Metathesaurus. "MetamorphoSys" facilitates exclusion of any vocabulary for which an additional license arrangement has not been negotiated, or to exclude vocabularies inappropriate to the purposes of the UMLS user.

UMLS Applications:

NLM and many other institutions are applying the UMLS Knowledge Sources in a wide variety of Applications including patient data creation, curriculum analysis, natural language processing, and information retrieval. NLM's own applications include PubMed ®, the NLM Gateway, ClinicalTrials.gov , and the Indexing Initiative.

An issue of NLM's Current Bibliographies in Medicine series, Unified Medical Language System (UMLS) covers the structure and semantics of the UMLS Knowledge Sources, their development and maintenance, and assessments of their coverage and utility for particular purposes, and the full range of UMLS applications. It contains 280 citations covering the period from January 1986 through December 1996. More recent references can be found by searching for Unified Medical Language System on MEDLINE ® /PubMed.

Obtaining the Knowledge Sources:

NLM does not charge for the UMLS products. They are available to U.S. and international users. Requestors must sign and submit a License Agreement for the Use of UMLS Products. Licensees are responsible for complying with the restrictions on use of the contents of the UMLS Metathesaurus detailed in the agreement. Some uses of some vocabularies contained in the Metathesaurus require separate agreements with the producers of the individual vocabularies.

All the Knowledge Sources are available to licensed UMLS users via the Internet from the UMLS Knowledge Source Server which has a Web interface and an applications program interface (API). ASCII relational files by ftp are available from the Server and may also be requested on CD-ROM. A complete description of the Knowledge Sources and their distribution formats can be found in the UMLS Documentation.

For additional information contact: E-mail: www.nlm.nih.gov/contacts/contact.html or 1-888-FINDNLM

A complete list of NLM Fact Sheets is available at:
(alphabetical list) www.nlm.nih.gov/pubs/factsheets/factsheets.html
(subject list): www.nlm.nih.gov/pubs/factsheets/factsubj.html

Or write to:

FACT SHEETS
Office of Communications and Public Liaison
National Library of Medicine
8600 Rockville Pike
Bethesda, Maryland 20894

Phone: (301) 496-6308
Fax: (301) 496-4450
email: publicinfo@nlm.nih.gov


Last updated: 18 July 2003
First published: 01 January 1988
Metadata | Permanence level: Permanent: Stable Content
Replaced by


U.S. National Library of Medicine, 8600 Rockville Pike, Bethesda, MD 20894 Copyright, Privacy, Accessibility
National Institutes of Health, Department of Health & Human Services