An online system receives an identification code for a product from a third party, which includes attributes that the third party uses to identify the product. The online system normalizes the identification code according to a set of guidelines received from the third party. The normalized identification code resembles previous identification codes received from the third party. The online system identifies a cluster of identification codes that represents the product identified by the normalized identification code by applying a set of matching rules to the normalized identification code and updates the identified cluster of identification codes to include the normalized identification code. The online system identifies a universal product identifier that represents the product of the cluster of the cluster of identification codes and stores the universal product identifier with the updated cluster of identification code.