Federated query

[Kamalraj Jairam]

Hello,

if i create federated query like

CONSTRUCT
{ ?s <http://localhost/target#patientId> ?o .}
WHERE
{ SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/traleerdf/csv#ID> ?o }
SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/db#patient_patientid> ?o }
}
LIMIT 10

will jena always send a select query to the endpoints?

I’m getting the following exception i execute this query

om.hp.hpl.jena.sparql.resultset.ResultSetException: skipToHead: Unexpected tag: {http://www.w3.or

[Andy Seaborne]

Post by Kamalraj Jairam
Hello,
if i create federated query like
CONSTRUCT
{ ?s <http://localhost/target#patientId> ?o .}
WHERE
{ SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/traleerdf/csv#ID> ?o }
SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/db#patient_patientid> ?o }
}
LIMIT 10
will jena always send a select query to the endpoints?
I’m getting the following exception i execute this query
om.hp.hpl.jena.sparql.resultset.ResultSetException: skipToHead: Unexpected tag: {http://www.w3.org/1999/02/22-rdf-syntax-ns#}RDF
Thanks
Kamalraj

Yes - SERVICE is always a SELECT, with HTTP headers for SPARQL results sets.

Andy

[Mark Feblowitz]

That reminds me of a question I have: for a DISTINCT result from the service, would one embed a SELECT DISTINCT within the SERVICE statement? Or is that assumed to be performed in the enclosing context?

Mark

Post by Andy Seaborne

Post by Kamalraj Jairam
Hello,
if i create federated query like
CONSTRUCT
{ ?s <http://localhost/target#patientId> ?o .}
WHERE
{ SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/traleerdf/csv#ID> ?o }
SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/db#patient_patientid> ?o }
}
LIMIT 10
will jena always send a select query to the endpoints?
I’m getting the following exception i execute this query
om.hp.hpl.jena.sparql.resultset.ResultSetException: skipToHead: Unexpected tag: {http://www.w3.org/1999/02/22-rdf-syntax-ns#}RDF
Thanks
Kamalraj

Yes - SERVICE is always a SELECT, with HTTP headers for SPARQL results sets.
Andy

[Rob Vesse]

You'd need to embed SELECT DISTINCT inside the SERVICE statement

SERVICE { Foo }

Translates to SELECT * WHERE { Foo } on the remote endpoint, Foo can be a
sub-query if you want to apply modifiers to the remote query

Rob

Post by Mark Feblowitz
That reminds me of a question I have: for a DISTINCT result from the
service, would one embed a SELECT DISTINCT within the SERVICE statement?
Or is that assumed to be performed in the enclosing context?
Mark

Post by Andy Seaborne

Post by Kamalraj Jairam
Hello,
if i create federated query like
CONSTRUCT
{ ?s <http://localhost/target#patientId> ?o .}
WHERE
{ SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/traleerdf/csv#ID> ?o }
SERVICE <http://localhost:8084/processor/webresources/rs/sparql>
{ ?s <http://localhost.com/db#patient_patientid> ?o }
}
LIMIT 10
will jena always send a select query to the endpoints?
I’m getting the following exception i execute this query
Unexpected tag: {http://www.w3.org/1999/02/22-rdf-syntax-ns#}RDF
Thanks
Kamalraj

Yes - SERVICE is always a SELECT, with HTTP headers for SPARQL results sets.
Andy