Unified Medical Language System® (UMLS®) Basics

The Lexical Tools

The lexical tools are a set of computer programs designed to aid in natural language processing. The three primary programs are:

• A lexical variant generator (LVG)
• A normalized string generator (Norm)
• A word Index generator (Wordind)

Together these programs address the high degree of variability in natural language words and terms. Words often have several inflected forms which would properly be considered instances of the same word. The verb "treat," for example, has three inflectional variants: "treats" the third person singular present tense form, "treated" the past and past participle form, and "treating" the present participle form. Multi-word terms in the Metathesaurus and other controlled vocabularies may have word order variants in addition to their inflectional and alphabetic case variants. The lexical tools allow the user to abstract away from this sort of variation.