Open Product Data 
To be able to check the quality of a global product data repository, some basic rules must be understood in order to create quality tools.
GTIN code control
Control of the format
The last digit of a GTIN code is computed using previous digits in order to avoid manual errors when the code is typed manually.
The algorithm is explained on the GS1 website at the following address : http://www.gs1.org/barcodes/support/check_digit_calculator
Control of the first 3 digits
The 3 first digit of the GTIN-13 code indicates the nature of the product or in the country in which it has been registered. The following list gives the correspondence: http://www.gs1.org/barcodes/support/prefix_list
If a GTIN-13 code starts with 3 digits not allowed by GS1, then this code can’t be integrated into the repository.