15. The method as recited in claim 14 , further comprising: determining a distribution entropy of a word under multiple categories; determining that the word is a stop word when the distribution of the word is higher than a threshold for stop word; and adding the word into the table of stop words.
15. The method as recited in claim 14 , further comprising: determining a distribution entropy of a word under multiple categories; determining that the word is a stop word when the distribution of the word is higher than a threshold for stop word; and adding the word into the table of stop words. 16. The method as recited in claim 15 , further comprising: ranking multiple words based on their respective distribution entropy under the multiple categories; and determining the threshold for stop word based on an order of the ranking.