12. A method for processing a search query having at least two search terms for searching for documents, the method comprising: expanding the query selecting one or more substitutable terms for at least one search term in the query; calculating a substitution probability for each substitutable term; for each substitutable term, calculating a co-occurrence probability with each of the remaining search terms in the search query; determining an occurrence probability for each substitutable term; calculating a score based on the combination of the substitution probability, the co-occurrence probability, and occurrence probability; and ranking the documents in an order determined by the score.
12. A method for processing a search query having at least two search terms for searching for documents, the method comprising: expanding the query selecting one or more substitutable terms for at least one search term in the query; calculating a substitution probability for each substitutable term; for each substitutable term, calculating a co-occurrence probability with each of the remaining search terms in the search query; determining an occurrence probability for each substitutable term; calculating a score based on the combination of the substitution probability, the co-occurrence probability, and occurrence probability; and ranking the documents in an order determined by the score. 21. The method of claim 12 , wherein documents are retrieved from a corpus based on the segmented terms and the substitutable terms of the query using a likelihood-type document retrieval process.