3. The computer readable storage medium according to claim 1 , further comprising instructions for: calculating weight values indicating strengths of combinations each term to obtain an m-by-n lexical mapping matrix T, which is defined as: 
 T=Q t P, wherein t represents the transposition of a matrix, and each weight value of the lexical mapping matrix T (W(r,i)) is defined as: W ⁡ ( r , i ) = ∑ k = 1 S ⁢ [ Exp ⁡ ( k , i ) ( Etf ⁡ ( i ) * Ewf ⁡ ( k ) ) ⁢ Naive ⁡ ( k , r ) ( Ntf ⁡ ( r ) * Nwf ⁡ ( k ) ) ] .
3. The computer readable storage medium according to claim 1 , further comprising instructions for: calculating weight values indicating strengths of combinations each term to obtain an m-by-n lexical mapping matrix T, which is defined as: 
 T=Q t P, wherein t represents the transposition of a matrix, and each weight value of the lexical mapping matrix T (W(r,i)) is defined as: W ⁡ ( r , i ) = ∑ k = 1 S ⁢ [ Exp ⁡ ( k , i ) ( Etf ⁡ ( i ) * Ewf ⁡ ( k ) ) ⁢ Naive ⁡ ( k , r ) ( Ntf ⁡ ( r ) * Nwf ⁡ ( k ) ) ] . 4. A computerized document processing system comprising a processor for performing the instructions of claim 3 .