15. A method as claimed in claim 1 , wherein the novelty score is determined on the basis of: p ij , which is the probability of the occurrence of n-gram i in document j determined from the extracted frequency of the n-gram i in the document j; q ij , which is the probability of occurrence of the n-gram i elsewhere in said documents determined from the extracted frequency of the n-gram i in the plurality of documents and the extracted frequency of the n-gram i in the document j; t ij , which is the probability of occurrence of the n-gram i in said documents determined from the extracted frequency of the n-gram i in the plurality of documents; S j , which is the total count of n-grams in the document j; and S, which is ΣS j , if p ij ≧q ij .
16. A method as claimed in claim 15 , wherein the novelty score is determined to be zero if p ij <q ij .