Each distinct product (i.e. each class of trade item) at each packaging level is assigned a Global Trade Item Number (GTIN) following GS1 identification standards. By adhering to GS1 standards, all products have a globally unique GTIN, so that any retailer is assured of having a unique way to refer to a given trade item, regardless of which products it carries (in contrast to a system where each brand owner devises its own identifiers), and each brand owner needs only to assign a single identifier to each of its products (in contrast to a system where each retailer uses its own identifiers)