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.
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. 21. The method as claimed in claim 20 , wherein a weighting is allocated in dependence upon the position in sequence of the common data item relative to the unmatched portion.