In indexing journals offering broad coverage of general medicine and specialties and in indexing sets of periodicals issued by different publishers, indexers usually rely on the external authority of a controlled vocabulary. Controlled vocabularies allow indexers to resolve variances in natural language systematically. The vocabularies establish preferred terms with cross-references from alternative forms of entry. Thus, all relevant references can be gathered under a single heading. Controlled vocabularies also establish hierarchical relationships among related terms. Such hierarchies most often take the form of a thesaurus in which narrower terms are entered as subentries beneath the broader terms to which they ...
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