14. One or more computer-readable non-transitory storage media embodying software that is operable when executed by one or more computing devices to: derive a concept matrix from a plurality of sample documents using singular value decomposition of a term-document matrix, the concept matrix identifying a latent pattern of word usage in the plurality of sample documents around a concept; derive concept terms by extracting significant terms from search text and inferring relevant terms therefrom using the concept matrix; and generate a first query for a first index of a first search engine and a second query for a second index of a second search engine, the first and second queries comprising at least one of the derived concept terms.
17. The media of claim 14 , the software further operable when executed by the one or more computing devices to cluster concept terms in synonym groups with an operator therebetween.