Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Unified Medical Language System® (UMLS®)

The Norm Program

The lexical program, Norm, generates the normalized strings for terms included in the SPECIALIST Lexicon. The normalization process involves stripping possessives, replacing punctuation with spaces, removing stop words such as "No Other Specification" or NOS, lower-casing each word, breaking a string into its constituent words, and sorting the words in alphabetic order.

Below is an example of the normalization process for the term Hodgkin's diseases, NOS.

Remove genitive Hodgkin diseases, NOS
Remove stop words Hodgkin diseases,
Lowercase hodgkin diseases,
Strip punctuation hodgkin diseases
Uninflect hodgkin disease
Sort words disease hodgkin


The Norm program is used in systems to:

  • Find similar terms
  • Map terms to UMLS concepts
  • Find lexical variants for a term

Download Lexical Tools, including the Norm program

Last Reviewed: July 29, 2016