[Rdfapi-php-interest] SPARQL FROM clause question

I would like to combine different ontology's resident in triple stores on
different servers. Eventually, thousands of them.
I am not certain but I suppose the SPARQL syntax provides for that. If not,
I can work around it in plain old PHP programming, issuing separate SPARQL
queries for separate servers, but I would like to know if that is the cours=
e
of action or not.
For example, I have two different SPARQL endpoints (they really exist):
http://www.15926.org/2006/02/oim and
http://www.15926.org/2006/02/rdl
with named graphs in them of the same names.

They are not, but suppose they are on different servers.
Now I want to combine them like this:

prefix dm: <http://www.15926.org/2006/02/dm#>
select ?id ?superclass
from <http://www.15926.org/2006/02/oim>
from <http://www.15926.org/2006/02/rdl>
where {
?id rdfs:subClassOf ?x .
?x owl:hasValue ?superclass .
?superclass rdf:type dm:ClassOfInanimatePhysicalObject .
}
Note: in RAP the namespaces rdfs, owl, and rdf don't need to be declared
with prefix.

The top two triples in the where clause work for the .../rdl graph and the
bottom for the .../oim graph.
This combined query doesn't work in RAP SPARQL (I'm using netapi).
My question is: should it work? Or would it work with different syntax? Or
totally not?

Onno Paap