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.