Term expansion refers to the process of replacing a single query term with one or more alternative terms, in order to increase retrieval results.

In addition to using stemming and morphology, some search engines expand query terms to a disjunction of related terms, using a thesaurus or some other similar data. Terms in a thesaurus can represent various types of relationships: equivalent (condo and condominium), synonymous (handbag and purse), strongly related (attack and ambush), moderately related (bloom and flower), etc.

By default, query terms are expanded using the ATG Search thesaurus. Users can control how much expansion to perform using query syntax (see the User-Entered Query Operators chapter) and user interface settings (see the Query Component Reference chapter). Administrators can add custom terminology to the thesaurus; this is useful for customer-specific product names, which might have various forms and models which should be retrieved from a single query term. Custom terminology is described in the Custom Terminology section.

Expansion allows users to move beyond literal keyword queries into a more sophisticated and effective search query. However, users may expect a simple keyword result, and be confused by additional results.

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