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United States National Library of Medicine National Institutes of Health

Fact Sheet
UMLS® MetamorphoSys


MetamorphoSys is the installation wizard and customization program included in each UMLS release. It installs one or more of the UMLS Knowledge Sources. If you select the Metathesaurus®, you can create customized Metathesaurus subsets.

Users customize their Metathesaurus subsets for two main purposes:

  1. to exclude vocabularies from output that are not required or licensed for use in a local application;
  2. to customize a subset using a variety of data output options and filters.

The Metathesaurus consists of a number of files, some of which are extremely large; excluding sources can significantly reduce the size of the output subset. Given the number and variety of vocabularies reflected in the Metathesaurus, it is unlikely that you would require all, or even most, of its more than 100 vocabularies. In addition, some sources require separate license agreements for specific uses, which you may not wish to obtain. These are clearly indicated in the Appendix to the License Agreement. Additional information about some source vocabularies may be found on the UMLS Homepage under Metathesaurus Source Vocabularies.


MetamorphoSys has been tested on the following operating systems: Sun Solaris 8 and 9, Macintosh (0S x 10.3 with current JRE from Software Update), Windows XP, NT, and 2000, and Linux (Red Hat Enterprise Linux WS, v. 3). It is implemented in Java and run-time environments for all platforms included in the release.

You may execute MetamorphoSys from the UMLS DVD-ROM (which contains the application and the compressed UMLS Knowledge Sources data files), or use a high-speed Internet connection to download files from the UMLS Knowledge Sources Server (UMLSKS). Because downloads on a T1 line with 1 megabit per second throughput will require over 5 hours, NLM expects that MetamorphoSys will usually be run from the DVD.

To use the DVD, you must have a DVD reader and at least 26GB of free disk space. Multiple runs that create multiple subsets of the Metathesaurus will need even more space. For reasonable performance, we suggest these minimum requirements:

DVD options allow you to copy the UMLS Knowledge Sources data files and/or MetamorphoSys .nlm format data files directly to local storage. This may be useful for multiple runs or subsetting an existing subset, and it may improve performance time.

A third option, Validate Distribution, allows you to verify the integrity of .nlm files downloaded from the UMLSKS or copied from the UMLS DVD. It compares downloaded file sizes to those in the release .CHK file, and is a useful first step for trouble-shooting when problems occur with a UMLS installation.

If the UMLS release is downloaded from the UMLSKS, there are four associated files:

The file is first unzipped to local storage and the MetamorphoSys application started.

Customization Components

Three pre-defined subsets assist you in creating useful and manageable output subsets during the installation process. You can modify these default subsets to include or exclude additional source vocabularies. MetamorphoSys also allows you to select one of two release formats, to choose 7-bit ASCII or the UTF-8 Unicode character set, to exclude data in specific languages, and to eliminate all concepts assigned to particular semantic types.

MetamorphoSys now includes a browser that allows you to view and search customized subsets created in Rich Release Format (RRF).

NLM invites suggestions regarding additional useful pre-defined subsets and other enhancements to MetamorphoSys. These can be sent to

More detail about installing, starting, and using MetamorphoSys is available in the UMLS Documentation.

A complete list of NLM Fact Sheets is available at:
(alphabetical list)
(subject list):

Or write to:

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

Phone: (301) 496-6308
Fax: (301) 496-4450

Last reviewed: 24 May 2006
Last updated: 24 May 2006
First published: 07 May 2004
Metadata| Permanence level: Permanent: Stable Content