Testing data consistency between graphs

Hi SWIG,

I've got an application that queries statements from an RDF database, and
in this process, the resulting graph might "lose" the IRI of a resource and
replace it with a bnode. (Specifically, my result is an RDFa document,
where an element with @typeof but no @about will produce a bnode, even if
it has an IRI in my data store). I want to ensure that the data in my
result graph is consistent with the data in the source graph:

The query result graph might only return a subset of the source data, which
is legal because of the Open World Assumption.

And (I presume) it's legal to substitute an IRI with a bnode (in the
subject & object positions). In this case, the statement is just saying
"Some resource exists with the given properties" which is still a true
statement.

I want to test that the data in my result graph is data also present in a
reference graph (my source database): that no IRIs were cast to literals,
that the lang/datatype on literals is preserved, and so on.

Graph isomorphism doesn't suffice, because bnodes are only matched with
bnodes. So first, is there a formally described function that does this? Or
else, what should it be called, perhaps "consistent with"?

And second, are there any other cases of applications modifying graphs to
replace an IRI with a bnode?

Thanks,

Austin.