6. A method as recited in claim 1 , further comprising: in response to determining that the rewritten keyword does not match any inquiry word in the search click log, classifying the input keyword into one or more characteristics; calculating a posterior probability of each of the one or more characteristics under each category in the search click log; and determining at least one category which posterior probability is higher than a preset threshold as a category that matches the input keyword.
6. A method as recited in claim 1 , further comprising: in response to determining that the rewritten keyword does not match any inquiry word in the search click log, classifying the input keyword into one or more characteristics; calculating a posterior probability of each of the one or more characteristics under each category in the search click log; and determining at least one category which posterior probability is higher than a preset threshold as a category that matches the input keyword. 7. A method as recited in claim 6 , wherein the one or more characteristics include one or more of: a product that determines whether the input keyword is a product name; a brand that determines whether the input keyword is a brand name; a model that determines whether the input keyword is a model name; a centric word in the input keyword; one or more nouns in the input keyword; the centric word and a noun left to the centric word; or the centric word and a noun right to the centric word.