Hi Francesco,
So you are saying if 2 D2R servers are using the initial ( or both ) query run
fine, but with Virtuoso initiating the federated query it fails querying
against the D2R server instance ? If so is this D2R server instance accessible
remotely such that we can try from here ?
Also, you can try turning on Virtuoso tracing to obtain more information on the
calls being made and error written to the log, using the trace_on() function [1]
[1] http://docs.openlinksw.com/virtuoso/fn_trace_on.html
<http://docs.openlinksw.com/virtuoso/fn_trace_on.html>
Best Regards
Hugh Williams
Professional Services
OpenLink Software, Inc. // http://www.openlinksw.com/
Weblog -- http://www.openlinksw.com/blogs/
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Universal Data Access, Integration, and Management Technology Providers
> On 7 Sep 2015, at 16:56, Francesco Balzu <i_ba...@hotmail.it> wrote:
>
> Hi !!
>
> I have a problem with the following query :
>
> select *
> where {
> ?sensor rdf:type km4c:SensorSite.
> ?sensor dcterms:identifier 'FI055ZTL00901'.
> SERVICE <http://localhost:2020/sparql <http://localhost:2020/sparql>>{
> SELECT ?sensor ?obs
> {
> ?obs km4c:isObservationOf ?sensor.
> } limit 10
> }
> }
>
> I get the following error:
>
> Virtuoso RDFZZ Error DB.DBA.SPARQL_REXEC('http://localhost:2020/sparql'
> <http://localhost:2020/sparql'>, ...) returned Content-Type 'text/html'
> status 'HTTP/1.1 400 Parse error: SELECT ?obs WHERE { ?obs .
> FILTER (isREF ( )) } Lexical error at line 3, column 19. Encountered: " " ('
>
>
>
> Error 400 Parse error:
> SELECT ?obs
> WHERE { ?obs .
> FILTER (isREF ( )) }
> Lexical error at line 3, column 19. Encountered: " " (32), after : "isREF"
>
> HTTP ERROR 400
> Problem accessing /sparql. Reason:
> Parse error:
> SELECT ?obs
> WHERE { ?obs .
> FILTER (isREF ( )) }
> Lexical error at line 3, column 19. Encountered: " " (32), after :
> "isREF"Powered by Jetty://
>
> The server running at http://localhost:2020 <http://localhost:2020/> is a D2R
> server and http://localhost:2020/sparql <http://localhost:2020/sparql> is a
> SPARQL endpoint.
> Initially I thought it was just a D2R error, but the strange thing is that if
> I select only ?obs inside the SERVICE clause, that is if I run the following
> query :
> select *
> where {
> ?sensor rdf:type km4c:SensorSite.
> ?sensor dcterms:identifier 'FI055ZTL00901'.
> SERVICE <http://localhost:2020/sparql <http://localhost:2020/sparql>>{
> SELECT ?obs
> {
> ?obs km4c:isObservationOf ?sensor.
> } limit 10
> }
> }
> I get the correct result. The problem with the latter query is that the
> variable sensor seems not bound to any value when the graph pattern inside
> the SERVICE clause is matched in D2R. That's why I'd prefer the former
> solution. The variable sensor should be bound to an IRI.
> If I run the former query from Fuseki server I get the correct result, so I
> was wondering why I'm not able to run it from Virtuoso.
> Maybe can't I query a D2R endpoint from a Virtuoso endpoint?
> Or do you think the problem is in D2R?
>
> Thanks a lot for your help and your time.
>
> Best Regards,
> Francesco Balzano.
>
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