1. A method of optimizing a value associated with a characteristic of a product stored in a first field of a security database of a self-checkout system at an optimizing time, said security database also including a second field for storing identification information for said product, a third field for storing a last time when said value was last updated and a fourth field for storing at least one new value for said characteristic stored in said fourth field between said last time and said optimizing time, said value being used in a comparison to a second value associated with said characteristic and detected in a security area of said self-checkout system during a purchasing transaction, said comparison used as a security measure to confirm that a product placed in said security area during said purchasing transaction is the same product identified by said system after said system identifies said product via identification information input by a user of said system, said method comprising: querying said database for products having a time difference between said optimizing time and said last time greater than a predetermined period and having at least one new value for said characteristic information, wherein said query establishes a query result; revising said value for each product in said query result using said new value.