Comments on SPARQL: Semantics of queries involving named graphs

Hi,

Can you clarify the query semantics for the following cases:

A SPARQL query can specify RDF dataset as follows:
FROM d1
FROM d2
...
FROM dn

FROM NAMED g1
FROM NAMED g2
...
FROM NAMED gm

Then the query may use graph clause in several ways:
1) GRAPH gx (explicit naming) => BUT, gx may not exist in {g1, g2, ..., 
gm}, then what is the expected behavior?
2) GRAPH ?g (variable-based naming)
    ?g may get instantiated from global (that is not enclosed inside a 
GRAPH clause) graph-pattern to a value gx (say)
    BUT gx may not be a member of {g1, g2, ..., gm}, then what is the 
expected behavior?

Thanks,

Jags