Federated SPARQL Query on a subgraph of a SPARQL endpoint - sparql

Question

I would like to ask, how to do a federated SPARQL query on a subgraph of a SPARQL endpoint (not the entire remote SPARQL endpoint).
I got my data in Virtuoso v7 while the SPARQL endpoint is "http://localhost:8890/sparql", I'd like to do a remote query on a subgraph of this endpoint which is "http://localhost:8890/TC", and I tried
SELECT *
WHERE
{ SERVICE <http://localhost:8890/sparql>
{ SELECT ?subject ?predicate ?object
FROM <http://localhost:8890/TC>
WHERE
{ ?subject ?predicate ?object }
}
} LIMIT 50
And I got the error that "FROM" is not correctly used, so I have two questions:
1) can I do a remote query on a subgraph of a SPARQL endpoint?
2) can I have a SPARQL endpoint for each graph in Virtuoso v7?
Thanks a lot for your help.

Answer 1

You can use graph instead of from.
In your example:
SELECT *
WHERE
{
SERVICE <http://localhost:8890/sparql>
{
SELECT ?subject ?predicate ?object
WHERE
{ graph <http://localhost:8890/TC> { ?subject ?predicate ?object } }
}
} LIMIT 50
I tested this syntax with the following query in the Uniprot SPARQL endpoint (Virtuoso) while federating with dbpedia (Virtuoso):
SELECT *
WHERE
{ SERVICE <http://dbpedia.org/sparql>
{select distinct ?activity where { graph <http://dbpedia.org> {?activity a <http://www.ontologydesignpatterns.org/ont/d0.owl#Activity>} } LIMIT 10
}
} LIMIT 50