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Glossary: Subject Headings and "Controlled Vocabulary"

Subject headings are used to help us locate the most relevant material because they represent the subject matter covered, usually using controlled vocabulary. Controlled vocabulary ensures that a term is used uniformly in every instance, so that if we find one item of use, a click on a subject heading will find other items with the same term. (That's important if we remember that computers search for letters rather than ideas.) It reduces the likelihood that we'll find irrelevant items in our results.

Subject headings are controlled because they're applied using a set of rules. A word is always in the same form - for instance it may always be a plural noun ("parties" rather than "party"). We don't need to worry about different authors expressing something in a different way because the database applies the terms uniformly.

TOPCAT uses the Library of Congress Subject Headings (LCSH) to identify the subject coverage of an item. This is a common system used in most academic libraries and by several databases.