Abstract: A system and associated methods identify documents relevant to an inputted natural-language user query. One associate method includes: selecting a set of keywords from the user query; determining at least one word, not necessarily found in the user query, that is semantically similar to a keyword of the set of keywords; using the set of keywords and the at least one word to determining a subset of word sets from a database of pre-stored word sets, wherein the pre-stored word sets are each pre-associated with at least one document; determining a plurality of word sets, from the subset of word sets, that is most semantically similar to the user query; and identifying documents that have been pre-associated with the plurality of word sets as being relevant to the natural-language user query.