1. A method of translating an input sequence of data items in a first format to an output sequence of data items in a second format using a store comprising a plurality of example sequences in the first format each paired with its translation in the second format, comprising: (a) choosing a base example sequence from the store based on a comparison of the input sequence with each of a plurality of example sequences from the store, and using its paired translation as a translation basis; (b) identifying a portion of the input sequence differing from a corresponding portion of the base example sequence, these portions being designated input and base example unmatched portions respectively; (c) locating a portion of the translation basis corresponding to the base example unmatched portion; (d) using the input unmatched portion to select a set of subsidiary example sequences from the store; (e) determining from the set of subsidiary example sequences a choice of possible translations corresponding to the input unmatched portion; (f) selecting a translation from the choice based on a predetermined selection algorithm and using the selected translation to replace the portion located in step (c); and (g) using the result of step (f) as a basis for the output sequence of data items.