2. A method as in claim 1 wherein: a first of said analysis algorithms is arranged to generate and compare word frequency lists and to produce a comparison result; and said predetermined algorithm includes forming from the reference corpus separate first and second parts, performing a comparison between said first and second parts in accordance with said first analysis algorithm, the resulting comparison result constituting a measure of the homogeneity of said first and second parts.
5. A method as in claim 2, including the steps of: presenting to the user, for each of a plurality of candidate documents stored in the retained text store, the respective dissimilarity measures and respective links to said plurality of stored retrieved texts, receiving from the user an allocated relevance value R in respect of a presented dissimilarity measure, and modifying said weights by multiplying each weight (Wi) by a respective weight factor (1+ki), where ki is a function of the contribution that the respective weighted comparison result makes to the dissimilarity measure, and the value of R-Rmean, where Rmean is the mean of lowest and highest possible relevance values.