1. A method of metering usage of software products on a data processing system, the method including the steps of: detecting an event indicative of the use of at least one product module on the system, checking on a catalogue, containing a plurality of product identifiers, if the at least one product module has a corresponding product identifier; if the at least one product module has no corresponding product identifier, determining a matching score indicative of the similarity of said product module with each of the plurality of product identifiers; responsive to the highest of said matching scores satisfying predetermined threshold criteria, adding an entry in the catalogue corresponding to said product module.