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Querying DBpedia with SPARQL and Jena


I cannot understand how can I query DBpedia using Jena. In the tutorials like here(Listing 4) model is initialized as follows:

// Open the bloggers RDF graph from the filesystem
InputStream in = new FileInputStream(new File("bloggers.rdf"));

// Create an empty in-memory model and populate it from the graph
Model model = ModelFactory.createMemModelMaker().createModel();
model.read(in,null); // null base URI, since model URIs are absolute
in.close();

Let's say I want to write a query that will list churches in Paris. In SPARQL it will look like (taken from this mailing list message):

PREFIX p: <http://dbpedia.org/property/>
PREFIX dbpedia: <http://dbpedia.org/resource/>
PREFIX category: <http://dbpedia.org/resource/Category:>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX geo: <http://www.georss.org/georss/>

SELECT DISTINCT ?m ?n ?p ?d
WHERE {
 ?m rdfs:label ?n.
 ?m skos:subject ?c.
 ?c skos:broader category:Churches_in_Paris.
 ?m p:abstract ?d.
 ?m geo:point ?p
 FILTER ( lang(?n) = "fr" )
 FILTER ( lang(?d) = "fr" )
 }

How will this query look in Java? Particularly, I'm interested in how the model object is initialized.


Solution

  • After browsing tons and tons of pages I found the answer. Perhaps I didn't ask the question clearly enough, but anyway below is the code that worked for me.

    String queryString=
    "PREFIX p: <http://dbpedia.org/property/>"+
    "PREFIX dbpedia: <http://dbpedia.org/resource/>"+
    "PREFIX category: <http://dbpedia.org/resource/Category:>"+
    "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>"+
    "PREFIX skos: <http://www.w3.org/2004/02/skos/core#>"+
    "PREFIX geo: <http://www.georss.org/georss/>"+
    
    "SELECT DISTINCT ?m ?n ?p ?d"+
    "WHERE {"+
    " ?m rdfs:label ?n."+
    " ?m skos:subject ?c."+
    " ?c skos:broader category:Churches_in_Paris."+
    " ?m p:abstract ?d."+
    " ?m geo:point ?p"+
    " FILTER ( lang(?n) = "fr" )"+
    " FILTER ( lang(?d) = "fr" )"+
    " }"
    
    // now creating query object
    Query query = QueryFactory.create(queryString);
    // initializing queryExecution factory with remote service.
    // **this actually was the main problem I couldn't figure out.**
    QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query);
    
    //after it goes standard query execution and result processing which can
    // be found in almost any Jena/SPARQL tutorial.
    try {
        ResultSet results = qexec.execSelect();
        for (; results.hasNext();) {
    
        // Result processing is done here.
        }
    }
    finally {
       qexec.close();
    }
    

    This answer I found on dbpedia-discussion of www.mail-archive.com page.