1. 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 in accordance with the concept matrix; and generate a query comprising a search expression having at least one of the derived concept terms.