1. A method performed in a Translation Memory Apparatus for 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) a processor of the apparatus 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) the processor 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 and other portions that are not the unmatched portions being designated input and base example matched portions respectively; (c) the processor locating a portion of the translation basis corresponding to the base example unmatched portion, wherein, when the portion of the translation basis corresponds to the base example unmatched portion and an adjacent base example matched portion, extending the base example unmatched portion to include the adjacent base example matched portion, and extending the corresponding input unmatched portion to include an adjacent input matched portion corresponding to the adjacent base example matched portion; (d) the processor using the input unmatched portion to select a set of subsidiary example sequences from the store; (e) the processor determining from the set of subsidiary example sequences a choice of possible translations corresponding to the input unmatched portion; (f) the processor 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) the processor using the result of step (f) as a basis for the output sequence of data items.