XDocument.DataAdapters.Count = 2
XDocument.DataObjects.Count = 0

The documentation seems to imply that you can't have one without the other.

Remarks
An external data source can take the form of a Microsoft Access or Microsoft
SQL Server database, an .xml file, or an XML Web service. The type of data
adapter object used to access the external data source depends on the type
of data source. The DataObject object provides a common set of properties
and a method that can be used for all types of data adapter objects, and
each of the data adapter objects provides its own set of properties and
methods.

Could someone clarify the relationship please.

Thanks,

Howard