Product Identifier

Definition

A product identifier is a code that names a product so that records can be matched: a seller’s own SKU, a global GTIN (the number under a barcode), or a marketplace’s catalogue number. They identify different things, so one item can have several codes, and one code can cover many variants.

In plain terms

A SKU (stock-keeping unit) belongs to one seller and means whatever that seller decided. A GTIN (known as UPC in North America and EAN elsewhere) is issued through GS1 and is meant to be unique to one product variant worldwide. A marketplace catalogue number (such as Amazon’s ASIN) is unique within that marketplace’s catalogue and may differ between its country stores.

Because each code lives in its own namespace, a safe key combines the namespace and the code, for example US-store:B0EXAMPLE1. A page address is not an identifier: it can change, and it often carries tracking parameters.

Example

One physical product as three systems know it (all codes invented; the GTIN has a valid check digit):

Matching the two sellers’ records by SKU would fail; matching by GTIN succeeds, if both recorded it.

Common misunderstandings

• “A SKU is globally unique.” It is unique only within one seller’s system; two sellers can use the same SKU for different things.
• “The page address identifies the product.” Addresses change and carry extra parameters; store the identifier, not the link.
• “One GTIN, one listing page.” A GTIN names a product variant; marketplaces may show it under several pages or group several GTINs on one page.