searches or searches through an electronic medical record. Entries may be one-word or multiple-word terms. Records contain four parts: base form (i.e. "run" for "running"); parts of speech (of which Specialist recognizes eleven); a unique identifier; and any available spelling variants. For example, a query for "anesthetic" would return the following: { base=anaesthetic spelling_variant=anesthetic entry=E0008769 cat=noun variants=reg } { base=anaesthetic spelling_variant=anesthetic entry=E0008770 cat=adj variants=inv position=attrib(3) } The SPECIALIST lexicon is available in two formats. The "unit record" format can be seen above, and comprises slots and fillers. A slot is the element (i.e. "base=" or "spelling variant=") and the fillers are the values attributable to that slot for that entry. The "relational table" format is not yet normalized and contain a great deal of redundant data in the files. Inconsistencies and other errors Given the size and complexity of the UMLS and its permissive policy on integrating terms, errors are inevitable. Errors include ambiguity and redundancy, hierarchical relationship cycles (a concept is both an ancestor and descendant to another), missing ancestors (semantic types of parent and child concepts are unrelated), and semantic inversion (the child/parent relationship with the semantic types is not consistent with the concepts). These errors are discovered and resolved by auditing the UMLS. Manual audits can be very time-consuming and costly. Researchers have attempted to address the issue through a number of ways. Automated tools can be used to search for these errors. For structural inconsistencies (such as loops), a trivial solution based on the order would work. However, the same wouldn't apply when the inconsistency is at the term or concept level (context-specific meaning of a term). This requires an informed search strategy to be used (knowledge representation). Supporting software tools In addition to the knowledge sources, the National Library of Medicine also provides supporting tools. Third party software UMLS-Similarity, an open source software package that implements many measures of semantic similarity and relatedness. UMLS-Similarity web interface, a web interface to UMLS-Similarity See also Medical classification References Further reading External links UMLS Summary description, with links to factsheets and documentation for Metathesaurus, Semantic Network, SPECIALIST Lexicon and MetamorphoSys UMLS Overview and Tutorial, by Rachel Kleinsorge, Jan Willis, Allen Browne, Alan Aronson A Perl module to query a UMLS mysql installation UMLS.me - extracts UMLS medical concepts and codes from free text in the browser, by Alexander Scarlat MD. Knowledge representation and reasoning Nursing classification