18. The method as claimed in claim 17 , wherein a preference value is determined by allocating a weighting to the or each such comparison, and combining the allocated weighting(s) in a predetermined manner.
18. The method as claimed in claim 17 , wherein a preference value is determined by allocating a weighting to the or each such comparison, and combining the allocated weighting(s) in a predetermined manner. 20. The method as claimed in claim 18 , wherein a weighting is allocated in dependence upon one or more of the following properties of a data item common to the input sequence and the subsidiary example: the position in sequence of the common data item; the frequency of the common data item in a predetermined corpus; the concurrence frequency of the common data item with the input unmatched portion; and the deviation of the concurrence frequency from that predicted by the frequency of the common data item and the input unmatched portion.