CODEWITHSUNDEEP
javasparqljena
Mogier
Mogier

Reputation: 31

Apache Jena - got 3 identical results for one query

This is my first question here on StackOverflow. I'm using Apache Jena in order to query DBPedia and the results i got are pretty strange. Here's my code, with a simple query :

    String sparqlQuery = "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> select ?o where { <http://dbpedia.org/ontology/Agent> rdfs:subClassOf  ?o}";
    System.out.println("Query : " + sparqlQuery);
    Query query = QueryFactory.create(sparqlQuery);
    QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query); 
    ResultSet results = qexec.execSelect();
    ResultSetFormatter.out(System.out, results, query);
    qexec.close();

And this is what i got in response :

<http://www.w3.org/2002/07/owl#Thing> <http://www.w3.org/2002/07/owl#Thing> <http://www.w3.org/2002/07/owl#Thing>

Any idea why i don't get a single Resource ? I tried with other Resources, same problem.

Thanks for your help and have a nice day !

Upvotes: 3

Views: 78

Answers (2)

NiziL
NiziL

Reputation: 5140

That's pretty strange, when I test your query on http://dbpedia.org/sparql, I got only one resource.

Can you check that there are three result in your ResultSet ?

int count = 0;
while( results.hasNext() ){
  results.next();
  count++;
}
System.out.println("I see "+count+" rows !");

As workaround, you could use the DISTINCT keyword:

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 
SELECT DISTINCT ?o
WHERE { 
  <http://dbpedia.org/ontology/Agent> rdfs:subClassOf  ?o
}

Upvotes: 2

AndyS
AndyS

Reputation: 16700

The query is sent to dbpedia so it is that giving three answers. Jena only formats the results.

It might be because there are 3 triples in different named graphs - the default dbpedia graph is the union of all named graphs.

Try: 

select *{ GRAPH ?g { <http://dbpedia.org/ontology/Agent> rdfs:subClassOf  ?o} }

Also check the results returns : issue the query with wget or curl and see the bytes sent back.

(The response you show does not correspond the ResultSetFormatter output)

Upvotes: 2

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