http://www.nlm.nih.gov/factsheets.dir/UMLS.html (Einblicke ins Internet, 10/1995)

Unified Medical Language System®

The purpose of the Unified Medical Language System (UMLS®) is to help health professionals and researchers to retrieve and integrate electronic biomedical information from a variety of sources, irrespective of the variations in the way similar concepts are expressed in different sources and despite the scattering of useful information among disparate computer systems.

The UMLS approach involves the development of machine-readable "Knowledge Sources" that can be used by a wide variety of applications programs to compensate for differences in the way concepts are expressed in different machine-readable sources and by different users, to identify the information sources most relevant to a user inquiry, and to negotiate the telecommunications and search procedures necessary to retrieve information from these sources. The goal is to make it easy for users to link information from patient record systems, bibliographic databases, factual databases, expert systems, etc.

The UMLS is not an attempt to create a single standard biomedical vocabulary. Nor is it a plan to develop a standard patient record format or to build a single unified medical knowledge base to assist with diagnosis and treatment.

UMLS Development Strategy

A long-term project of the breadth and complexity of the UMLS requires the knowledge and skills of experts in many fields. For this reason the UMLS development strategy involves a combination of internal research and development at NLM itself, competitively awarded contracts for research assistance with several U.S. research groups, and advice from professional associations and other interested groups in the private sector. Research and development related to the UMLS is fundable under NLM's grant programs and under the National Science Foundation's Program in Database Activities in Biological, Behavioral, and Social Sciences, as well as special UMLS-related requests for contract proposals.

UMLS Components

There are now four UMLS knowledge sources: a Metathesaurus®, a Semantic Network, an Information Sources Map, and the SPECIALIST Lexicon. The Metathesaurus contains information about biomedical concepts, their representation in different vocabularies and thesauri, and their use and co-occurrence in selected databases. The Metathesaurus represents a variety of relationships among terms and can support mapping from the user's terms to appropriate controlled vocabularies. The Semantic Network contains information about the types or categories (e.g., "Disease or Syndrome," "Virus") of terms in the Metathesaurus and the permissible relationships among these types (e.g., "Virus" causes "Disease or Syndrome"). The Information Sources Map or directory contains both human-readable and machine-"processable" information about the scope, location, vocabulary, syntax rules, and access conditions of biomedical databases of all kinds. The Lexicon contains syntactic information for many Metathesaurus terms, component words, and English words, including verbs, that do not appear in the Metathesaurus.

The UMLS knowledge sources are designed for use by system developers in a variety of biomedical and health-related environments. Although it will probably be necessary to create local addenda to support particular applications, the use of the central UMLS knowledge sources should substantially reduce the level of effort required to build effective user interfaces to biomedical information.

The four UMLS knowledge sources are designed for use by intelligent interface programs in interactions with users as well as in interactions with available files of machine-readable biomedical information. By using the UMLS Knowledge Sources, such programs should eventually be able to analyze user input; to select sources likely to contain information relevant to user queries; to help refine user queries and translate them into the syntax suitable for searching relevant databases; and to merge, organize, evaluate, and rank the information retrieved according to its relevance to the user's query.

Multiple interface programs that make use of the UMLS Knowledge Sources are being developed, each tailored to the needs of particular groups of users or to specific hardware and software environments. NLM itself is using the UMLS Knowlege Sources to develop better interfaces to its MEDLARS® databases. Other interfaces that make use of the UMLS knowledge sources are being developed by other institutions and private companies.

Arrangements for Distribution of UMLS Components

To ensure that UMLS components get actual use as soon as possible, they are being developed through a series of successive approximations of the capabilities ultimately desired. Expansions in scope and complexity are based on feedback received from those making use of the experimental versions.

NLM encourages broad experimentation with the fourth experimental edition of the UMLS Knowledge Sources. Those who wish to test the application of these tools in particular biomedical information environments are required to sign a one-year experimental agreement with NLM which may be extended when new experimental editions of the UMLS Knowledge Sources are issued. The general provisions of the agreement are as follows:

There is no charge for the UMLS products for the duration of the experimental agreement, although there may be a charge for subsequent versions of UMLS products.
Recipients of the UMLS products must provide feedback to NLM on how the products are being used and on any changes or enhancements that would make them more useful.
Recipients of the UMLS products may not redistribute them except as an integral part of the computer applications they develop.
Recipients of the UMLS products are responsible for complying with copyright restrictions that apply to some of the contents of the UMLS Metathesaurus.

Users of the experimental editions of the UMLS Knowledge Sources should be aware that there may be changes in the content or format of subsequent versions of the UMLS products.

Distribution Formats

The UMLS Knowledge Sources are available in multiple formats on four CD-ROMs, including an ASCII "relational" format, and, for the Metathesaurus, browsable versions usable on Apple Macintosh computers and on DOS-based PCs. Some lexical programs useful in matching local vocabularies, free-text, or user queries to the Metathesaurus are also distributed on the CDs.

The Metathesaurus files occupy more than 600 megabytes of storage. The other UMLS Knowledge Sources are relatively small. Sample sets of records from the UMLS Knowledge Sources are available on an Internet ftp service. The complete files are available on CD-ROM only.

Application Procedures

Those interested in obtaining copies of the initial UMLS products under the terms outlined above may obtain sample records, documentation, and copies of the experimental agreement to request these materials from the NLM anonymous ftp file service at nlmpubs.nlm.nih.gov (UMLS files and documents are located in the umls section of the nlmpubs directory) or write to:

Betsy L. Humphreys
UMLS Project Officer
National Library of Medicine
8600 Rockville Pike
Bethesda, MD 20894
FAX 301/496-4450

To obtain the complete versions of the UMLS Knowledge Sources, individuals or institutions must sign and return the experimental agreement.

Other facts sheets in the UMLS series:

Printed Copies are available from:

Office of Public Information
National Library of Medicine
8600 Rockville Pike
Bethesda, Maryland 20894

NLM HyperDOC / Unified Medical Language System / May 1994