17. A method as claimed in claim 16 , wherein the novelty score is determined on the basis of the following: Ψ ij = { ( S j * p ij * ln ⁢ ⁢ p ij ) + ( ( S - S j ) * q ij ⁢ *) - ( S * t ij * ln ⁢ ⁢ t ij ) , p ij ≥ q ij 0 , } ⁢ P ij ≥ q ij P ij < q ij where Ψ ij is the novelty score of the n-gram i in the document j.
16. A method as claimed in claim 15 , wherein the novelty score is determined to be zero if p ij <q ij .