16. A computer information system, comprising: a first search engine having a first index; a second search engine having a second index different from said first index; and a computer readable memory encoded with logic that when executed by a processor is operable to perform operations comprising: deriving concept terms by extracting significant terms from search text and inferring relevant terms from the extracted significant terms using a concept matrix, the concept matrix derived 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, the concept matrix further providing a term-term similarity between the search text and terms in the plurality of sample documents; and generating a first query for said first index and a second query for said second index, the first and second queries comprising search expressions having at least one of the derived concept terms.
16. A computer information system, comprising: a first search engine having a first index; a second search engine having a second index different from said first index; and a computer readable memory encoded with logic that when executed by a processor is operable to perform operations comprising: deriving concept terms by extracting significant terms from search text and inferring relevant terms from the extracted significant terms using a concept matrix, the concept matrix derived 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, the concept matrix further providing a term-term similarity between the search text and terms in the plurality of sample documents; and generating a first query for said first index and a second query for said second index, the first and second queries comprising search expressions having at least one of the derived concept terms. 19. The computer information system as recited in claim 16 wherein the logic is further operable to cluster concept terms in synonym groups with an operator therebetween.