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From Alessandro Adamou <ada...@cs.unibo.it>
Subject Re: SPARQL path query with JenaSparqlEngine
Date Mon, 06 Feb 2012 12:04:38 GMT
Hi,

perhaps some more information is needed in order to understand why I'm 
getting this?

I don't know if it can be useful to check the actual dataset: it's a 
partial dataset obtained by querying the Revyu SPARQL endpoint

Best,
Alessandro


On 1/31/12 12:12 PM, Alessandro Adamou wrote:
> Hi, I tried to execute this query - path of length 2 - on a partial 
> dump of Revyu, using a JenaSparqlEngine registered with QueryParser:
>
> SELECT  ?r0 ?x0  ?r1
> WHERE {
> <http://semanticweb.org/dumps/people/teddypolar> ?r0 ?x0 .
>  ?x0 ?r1 
> <http://semanticweb.org/dumps/things/alcazar-food-fun-and-music-in-paris>
> }
>
> and got the RuntimeException whose partial trace is attached at the 
> end of this message:
>
> java.lang.RuntimeException: cannot convert 
> "dcc31c09026e5a3aee0b63cb44a07ff8a76d1449" to NonLiteral
>
> Indeed it is because the value 
> "dcc31c09026e5a3aee0b63cb44a07ff8a76d1449" (for ?x0) is an untyped 
> literal, so no paths con be constructed there. Still I hoped datatype 
> and annotation assertions would be skipped instead of throwing 
> exceptions.
>
> So I thought I could just make the second step in the path OPTIONAL  - 
> after all I need shorter paths too - like this:
>
> SELECT  ?r0 ?x0  ?r1
> WHERE {
> <http://semanticweb.org/dumps/people/teddypolar> ?r0 ?x0
> OPTIONAL {
>  ?x0 ?r1 
> <http://semanticweb.org/dumps/things/alcazar-food-fun-and-music-in-paris>
> }
> }
>
> ... but I just get the same exception.
>
> This very same query (with OPTIONAL) on other SPARQL engines, such as 
> the TopBraid Composer one, terminates and delivers the expected results.
>
> Is there a clue as to how this query can be executed "safely", without 
> forcing conversion of literals?
>
> Thanks!
>
> Alessandro
>
>
> ------- EXCEPTION TRACE FOLLOWS --------
>
> java.lang.RuntimeException: cannot convert 
> "dcc31c09026e5a3aee0b63cb44a07ff8a76d1449" to NonLiteral
>         at 
> org.apache.clerezza.rdf.jena.commons.Jena2TriaUtil.convertNonLiteral(Jena2TriaUtil.java:127)
>         at 
> org.apache.clerezza.rdf.jena.facade.JenaGraph.filter(JenaGraph.java:123)
>         at 
> org.apache.clerezza.rdf.jena.facade.JenaGraph.graphBaseFind(JenaGraph.java:151)
>         at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:240)
>         at 
> com.hp.hpl.jena.graph.impl.GraphBase.graphBaseFind(GraphBase.java:260)
>         at com.hp.hpl.jena.graph.impl.GraphBase.find(GraphBase.java:257)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterTriplePattern$TripleMapper.<init>(QueryIterTriplePattern.java:67)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterTriplePattern.nextStage(QueryIterTriplePattern.java:41)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.makeNextStage(QueryIterRepeatApply.java:91)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.hasNextBinding(QueryIterRepeatApply.java:52)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterBlockTriples.hasNextBinding(QueryIterBlockTriples.java:53)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterDefaulting.hasNextBinding(QueryIterDefaulting.java:43)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterRepeatApply.hasNextBinding(QueryIterRepeatApply.java:57)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIterConvert.hasNextBinding(QueryIterConvert.java:49)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:28)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorWrapper.hasNextBinding(QueryIteratorWrapper.java:28)
>         at 
> com.hp.hpl.jena.sparql.engine.iterator.QueryIteratorBase.hasNext(QueryIteratorBase.java:66)
>         at 
> com.hp.hpl.jena.sparql.engine.ResultSetStream.hasNext(ResultSetStream.java:57)
>         at 
> org.apache.clerezza.rdf.jena.sparql.ResultSetWrapper.<init>(ResultSetWrapper.java:39)
>         at 
> org.apache.clerezza.rdf.jena.sparql.JenaSparqlEngine.execute(JenaSparqlEngine.java:68)
>         at 
> org.apache.clerezza.rdf.core.access.TcManager.executeSparqlQuery(TcManager.java:272)
>
>
>


-- 
M.Sc. Alessandro Adamou

Alma Mater Studiorum - Università di Bologna
Department of Computer Science
Mura Anteo Zamboni 7, 40127 Bologna - Italy

Semantic Technology Laboratory (STLab)
Institute for Cognitive Science and Technology (ISTC)
National Research Council (CNR)
Via Nomentana 56, 00161 Rome - Italy


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and so I am beyond caring."
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