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. 8. A method as recited in claim 6 , wherein calculating the posterior probability of each of the one or more characteristics under each category comprises using a formula of p ⁡ ( y | x ) = 1 Z ⁡ ( x ) ⁢ exp ( ∑ j ⁢ ⁢ λ j ⁢ f j ⁡ ( x , y ) ) , wherein: y represents a respective category in the search click log; x represents the input keyword; f j (x, y) represents a j th characteristic of x under the respective category y; λ j represents a weight of the j th characteristic; and Z(x) represents a normalization factor.