To distinguish between objects every object needs a unique identifier. This can be a number, a GUID or any other kind of ID. The supplier of the inventory management system determines the identifier and it should always be part the data record. It has to be unique within the stock of the advertiser, but one can also opt for having it unique for all objects of all advertisers.
DV needs to know if the object identifier can be used as a reference number for advertisements. If an advertiser can quickly find an object in the inventory management system using the object identifier it will be publicly displayed on advertisements (where possible). If the object identifier is purely used for the communication with DV and has no meaning for the advertiser it will not be published.
Each object has a unique automatically generated Hexon identifier as well. These are not used in communicating with the supplier of the inventory management system.