Consider a sequence of characters: , the MI of characters and is computed by equation 5: is the occurrence probability of the character sequence , which is estimated by the number of times that is followed by , normalized by N which is the total number of words in the corpus.
is the probability of character which is estimated by the total occurrences of the word normalized by N, namely: equation 5 is represented as follows: 3 WS under Chinese Sign Language Environment In the course of WS, efficiency will be reduced gradually with the increase of the length of sentence, so it performs the preprocessing to the target text got from the Web.