The Unified Medical Language System (UMLS) is a compendium of many controlled vocabularies in the biomedical sciences (created 1986).
[1] It provides a mapping structure among these vocabularies and thus allows one to translate among the various terminology systems; it may also be viewed as a comprehensive thesaurus and ontology of biomedical concepts.
The purpose of the UMLS is to enhance access to this literature by facilitating the development of computer systems that understand biomedical language.
[citation needed] Users of the system are required to sign a "UMLS agreement" and file brief annual usage reports.
Some examples of the incorporated controlled vocabularies are CPT, ICD-10, MeSH, SNOMED CT, DSM-IV, LOINC, WHO Adverse Drug Reaction Terminology, UK Clinical Terms, RxNorm, Gene Ontology, and OMIM (see full list).
Numerous relationships between the concepts are represented, for instance hierarchical ones such as "isa" for subclasses and "is part of" for subunits, and associative ones such as "is caused by" or "in the literature often occurs close to" (the latter being derived from Medline).
The major semantic types are organisms, anatomical structures, biologic function, chemicals, events, physical objects, and concepts or ideas.
The links among semantic types define the structure of the network and show important relationships between the groupings and concepts.
Phrased differently, they capture the fact that a corresponding relational assertion is meaningful (though it need not be true in all cases).
Each entry contains syntactic (how words are put together to create meaning), morphological (form and structure) and orthographic (spelling) information.
Given the size and complexity of the UMLS and its permissive policy on integrating terms, errors are inevitable.