The Search Service allows you to create a thesaurus (or synonym list), load it into the server, and enable thesaurus expansion for all user queries. Thesaurus expansion allows a term or phrase in a user’s search to be replaced with a set of custom related terms before the actual search is performed. This feature improves search quality by handling unique, obscure, or industry-specific terminology.

For example, with conventional keyword matching, a search for the term “web applications” might not return documents that discuss portlets or web services. However, by creating a thesaurus entry for “web applications,” it is possible to avoid giving users zero search results because of differences in word usage. The entries allow related terms or phrases to be weighted for different contributions to the relevance ranking of search results. For example, “web applications” is not really a synonym for web services, so a document that actually contains web applications should rank higher than one that contains web services.

web applications,portlets,web services[0.5]

In this example, the number [0.5] corresponds to a non-default weighting for the phrase web services.

Thesaurus entries can be created to link closely related terms or phrases, specialized terminology, obsolete terminology, abbreviations and acronyms, or common misspellings. The expansion works by simply replacing the first term in an entry with an OR query consisting of all the terms or phrases in the entry. The weights are then taken into consideration when matching search results are ranked.

The thesaurus expansion feature is best used for focused, industry- or domain-specific examples. It is not intended to cover general semantic relationships between words or across languages, as with a conventional paper thesaurus. Although the Search Service thesaurus expansion can definitely improve search quality, adding entries for very general or standard terms can actually degrade search quality if it leads to too many search result matches.