A method of locating relevant documents wherein documents are given a fingerprint comprising weights associated with particular topic categories of a classification system, each weight representing a degree to which the document relates to the particular topic category. Documents whose fingerprints have a predetermined degree of mathematical overlap with the fingerprint may be considered relevant. Fingerprints of texts may be combined to define user fingerprints and user fingerprints may be combined to define community user fingerprints, which can be monitored. Changes in the interest of the online community may be monitored and automatically reported to advertisers who can then instantly adjust their advertising campaign. Similarly, changes in community interest may be reported to pharmaceutical companies monitoring drug side effects. The methods may be used in combination with keyword searching.