Why use a thesaurus? Simply stated, the primary purpose of a thesaurus is to match the terms employed by the user with the terms chosen by the indexer. In this manner, an item or a concept is always defined by a single unique term with links to synonyms or related terms. Using this method, a user is sure to find all possible items relating to a concept since they are each associated with one of a linked group of synonymous terms. For example, a user searching for items on corn may not know whether to use corn or maize. To ensure that the user retrieves all terms relating to corn, the database or web site should use the descriptor corn and create a reference from maize to corn. Thesauri normally employ a mechanism called authority control when establishing terminology and creating references among terms.