A method of optimizing attribute information of a product attribute stored in a product database is provided. The product database includes update information comprising a time that the attribute information has last been updated and correction history information including recorded samples of new attribute information. The attribute information is used as a security measure in a self-checkout purchasing system to confirm that a purchased product is the same product identified by the system after identification information of the product is input by a user of the system. The method includes conducting a query of the database for any products having said update information older than a predetermined period of time, having correction history information, and where the history information includes a plurality of recorded samples greater than a predetermined amount. The query establishes a query result, whereby revised attribute information is then calculated using the plurality of the recorded samples as data. The revised attribute information is then stored as the current attribute information at a time which replaces the time information contained in the database relating to the time the attribute information was last updated.