1. A method for indexing and retrieving documents stored in a database, comprising: extracting a document feature vector for each of a plurality of documents; projecting each document feature vector to a low dimension document feature vector; indexing each of the plurality of documents according the associated low dimension document feature vector in the database; representing a spoken query as a lattice, the lattice representing likely possible sequential combinations of words in the spoken query; converting the lattice to a query certainty vector; projecting the query certainty vector to an associated low dimension query certainty vector; comparing the low dimension query vector to each of the low dimension document feature vectors; and retrieving a result set of documents from the database that have low dimension document feature vectors that match the low dimension query certainty vector.