34. The computer-readable memory device of claim 28 , where the variation of context in which the sequence occurs is calculated relative to a collection of documents.
34. The computer-readable memory device of claim 28 , where the variation of context in which the sequence occurs is calculated relative to a collection of documents. 37. The computer-readable memory device of claim 34 , where the variation of context in which the sequence occurs, HC(S), is calculated as 
 HC ( S )=MIN( HLC ( S ), HRC ( S )), where MIN defines a minimum operation, S represents the sequence, HLC(S) is defined as ∑ w ⁢ δ ⁡ ( wS ) and HRC(S) is defined as ∑ w ⁢ δ ⁡ ( Sw ) , where δ(X) is defined as one if sequence X occurs in the collection of documents and zero otherwise, where wS refers to word w followed by the sequence S, and where Sw refers to the sequence S followed by the word w.