The tokenized query, as well as each query alternative generated by spelling suggestion, is expanded by the MDEX Engine based on thesaurus matches. This topic describes the behavior of the thesaurus expansion feature.

Thesaurus expansion replaces each expanded query term with an OR of alternatives.

For example, if the thesaurus expands pentium to intel and laptop to notebook, then the query pentium laptop will be expanded to:

(pentium OR intel) AND (laptop OR notebook)

assuming the match mode is MatchAll.

The other match modes (with the exception of MatchBoolean) behave analogously.

If there is a multiple-word thesaurus match, then OR is used on the query itself to accommodate the various ways of partitioning the query terms.

For example, if high speed expands to performance, then the query high speed laptop will be expanded to:

(high AND speed AND (laptop OR notebook)) OR (performance 
AND (laptop OR notebook))

Multiple-word thesaurus matches only apply when the words appear in exact sequence in the query. The queries speed high laptop and high laptop speed do not activate the expansion to performance.