10. A method of organising and storing documents in a computer system for subsequent retrieval, the documents having associated metadata terms, the method comprising: providing access to a store of existing metadata in the computer system; analysing the existing metadata to generate statistical data as to co-occurrence of pairs of terms in the metadata of a single document; analysing a fresh document to assign to the fresh document a set of terms and determine for each term of the set a measure of a strength of association of the term with the document; determining for each term of the set a score that is a monotonically increasing function of (a) the strength of association with the document and of (b) a relative frequency of co-ocurrence, in the existing metadata, of the term and another term that occurs in the set; and selecting, as metadata for the fresh document, a subset of the terms in the set having highest scores.
10. A method of organising and storing documents in a computer system for subsequent retrieval, the documents having associated metadata terms, the method comprising: providing access to a store of existing metadata in the computer system; analysing the existing metadata to generate statistical data as to co-occurrence of pairs of terms in the metadata of a single document; analysing a fresh document to assign to the fresh document a set of terms and determine for each term of the set a measure of a strength of association of the term with the document; determining for each term of the set a score that is a monotonically increasing function of (a) the strength of association with the document and of (b) a relative frequency of co-ocurrence, in the existing metadata, of the term and another term that occurs in the set; and selecting, as metadata for the fresh document, a subset of the terms in the set having highest scores. 16. The method according to claim 10 , in which the score for a term is proportional to the square root of a number a number representing how many terms have been assigned to the document and also have nonzero weights in the set of weights for that term.