7. A method of generating a language model, said method comprising: (i) providing a reference corpus; (ii) forming from said reference corpus a training portion and a development portion; (iii) generating initial values of respective weights corresponding to a plurality of analysis algorithms by processing the training portion in accordance with a predetermined algorithm; (iv) performing a comparison between the training portion and the development portion in accordance with a first of said analysis algorithms and producing an initial comparison result, said first analysis algorithm being arranged to generate and compare word-level n-gram frequency lists having n-grams from unigrams up to m-grams, where m is a predetermined integer, the word-level n-gram frequency list generated from the training portion constituting a language model; (v) performing information retrieval in accordance with steps (d) to (h) of the method of claim 1, using the above mentioned plurality of analysis algorithms, and using the training portion as the reference corpus; (vi) retrieving a document from the retained text store; (vii) modifying the training portion by combining it with the document retrieved from the retained text store; (viii) repeating step (iv) in respect of the modified training portion to produce a further comparison result; and (ix) modifying the weights in accordance with a weight modifying function of said initial and further comparison results.
9. A method as in claim 7 wherein step (vi) comprises selecting the document for retrieval on the basis of the least degree of dissimilarity.