When you federate a SPARQL query to an allowed SPARQL endpoint that contains named graphs, such as the Europeana one, with a query that references any named graphs, you get the error Unknown error: Use of WITH and GRAPH constructs in query body is not supported in triples mode. For example, the following query replicates the error:
ASK {
SERVICE <http://sparql.europeana.eu> {
GRAPH ?g {
[] ?p [] .
}
}
}The full stack is here:
Caused by: com.bigdata.rdf.sparql.ast.QuadsOperationInTriplesModeException: Use of WITH and GRAPH constructs in query body is not supported in triples mode.
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.fillInIV(ASTDeferredIVResolution.java:1039)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.fillInIV(ASTDeferredIVResolution.java:896)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.fillInIV(ASTDeferredIVResolution.java:896)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.fillInIV(ASTDeferredIVResolution.java:1052)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.fillInIV(ASTDeferredIVResolution.java:896)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.prepare(ASTDeferredIVResolution.java:669)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.resolve(ASTDeferredIVResolution.java:454)
at com.bigdata.rdf.sparql.ast.eval.ASTDeferredIVResolution.resolveQuery(ASTDeferredIVResolution.java:268)
at com.bigdata.rdf.sparql.ast.eval.ASTEvalHelper.optimizeQuery(ASTEvalHelper.java:408)
The error is happening here:
This will be addressed with the move to an alternative backend (https://phabricator.wikimedia.org/T206560). A test case for this particular problem will be added to the WDQS Testing (https://wikitech.wikimedia.org/wiki/User:AndreaWest/WDQS_Testing).