Unique product identifiers are product codes or other values associated with an individual product. The primary set of unique product identifiers are Global Trade Item Numbers (GTINs), which include UPC,EAN (in Europe), JAN (in Japan) and ISBN. In addition, a Manufacturer Part Number (MPN) can be used to identify a specific product in the 'mpn' attribute if it is accompanied by the manufacturer's brand name in the 'brand' attribute.
The category/product type you submit products to will determine what Unique Identifiers you need to submit with your data. By default, PowaWEB submits your product type as ‘N/A’ but you can override this using the Customer Product Attributes. If you do override this, Google provide exact information on what is required for each category/product type in the blog under the section ‘Including Unique Product Identifiers in your Data’:http://www.google.com/support/merchants/bin/answer.py?answer=160161
How do I know what the Unique Product Identifier is for my product?
If you don’t have the identifier data, you can find it on the Product Search "Compare prices" pages under the “technical specifications” section for Electronics items, the "Tracks" or "Details" section for Media and the “Overview” section for books.
You can look up UPCs or EANs at the Internet UPC Database website, which includes many, though not all, product identifiers that have been issued. You can look up ISBNs at ISBNdb.com. You can also check ISBN-13 on Google Product Search.
Note: Please do not invent or approximate values for GTIN, MPN or Brand. Each has a prescribed value assigned by the manufacturer and any other value will be flagged as invalid.
Add Unique Identifiers and the Product Type attribute to your products
Starting from 20.06.2011, unique identifiers for all products except apparel and one-of-a-kind items will be required. See http://googlemerchantblog.blogspot.com/2011/05/enforcement-of-our-unique-identifier_03.html .
By default our system passes 'Brand' to Google Merchant Center, so you will need to add GTIN and/or MPN attributes to your products manually, depending on which Product Type you associate with your product.
1. In the PowaWEB Dashboard go to Manage Catalogue > Manage Products > Edit Product > Custom Attributes.
2. Click on Add Attribute to create corresponding attributes. The expected format (name/value) can be found here: http://www.google.com/support/merchants/bin/answer.py?hl=en&answer=188494&expand=GB
For example, if you need to add the ISBN attribute, you will need to enter gtin as the custom attribute name and, e.g., 0451524233 as its value.
3. By default the system pass 'n/a' as the value for the Product Type attribute, so where appropriate we recommend you override this value by adding a custom attribute with the name 'product_type' to your products. The expected value format can be found here:http://www.google.com/support/merchants/bin/answer.py?hl=en&answer=188494&expand=GB
For example, if you need to specify the following product type: Home & Garden > Kitchen & Dining > Appliances > Refrigerators, you will need to enter product_type as the custom attribute name and Home & Garden > Kitchen & Dining > Appliances > Refrigerators as its value.
See also Custom Product Attributes and What custom attributes can be passed to Google Merchant Center for more information on this topic.