How to link a dataset to its superset?

Hello,

The VoID vocabulary can be used to describe RDF datasets, and can be used
to specify that one dataset is a subset of another dataset. But what is the
proper/best way for the inverse relationship - saying that a dataset is a
superset of the other?

An example:

ex:DatasetA a void:Dataset;
  void:subset ex:DatasetB
.

ex:DatasetB a void:Dataset;
  ? ex:DatasetA
.

What could be put at the question mark? VoID has the property
void:inDataset, but it has foaf:Document as its domain. So it can only be
used for documents, not for any dataset. Dcterms:isPartOf is another
possibility, but it is a very general property which could already be in
use for other purposes in the same dataset. Also, it seems kind of funny
hat the two inverse relationships come from different vocabularies. Could
there be something better?

If there is no ideal solution, I wonder if there at least is a common
practice.

Regards,
Frans