Default Graph Contents

Yesterday in the working group conference call we did not directly answer
this R2RML question:

For a SPARQL query that does not specify any "FROM <x>" or "FROM NAMED <x>"
or "GRAPH <x>" clauses, what is expected to be in the default dataset for
this query? I can think of a few possible  answers:

1) Only those triples defined by the mapping to be in the unnamed graph
2) All of the triples defined by the mapping (including those produced in
the unnamed graph as well as in named graphs)
3) This is an implementation specific detail that R2RML does not address

A related issue is whether an implementation is allowed to add triples
(either in the unnamed graph or a named graph). For example, can an
implementation add triples that are metadata describing the relational
database or the mapping itself. This would be roughly analogous to the
"system" tables provided by relational databases.

-David