In order for the site to know who is advertising an object, DV usually includes an account identifier with the advertisement. This identifier can be a number, GUID or any other kind of ID determined by the site (for example the account number or login name of the advertiser on the site). If preferred the identifier can be determined by DV instead. The site then needs to convert this identifier to its own internal account identifier. The way these identifiers are exchanged is explained in section III.6.1. New advertiser.
The account identifier does not necessarily need to be part of the mutation (as a data field). It can also be sent as part of the batch file name or the endpoint URI for example.
It is possible for multiple advertisers to share the same account identifier, for example, if two outlets of the same company wants to advertise as one company. Conversely it is also possible, though not common, for one advertiser to advertise using multiple account identifiers.