使用SPARQL和Jena查询DBpedia [英] Querying DBpedia with SPARQL and Jena

问题描述

我不明白如何使用耶拿(Jena)查询DBpedia.在类似此处(清单4)的模型中初始化如下:

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();

假设我想编写一个查询，该查询将列出巴黎的教堂.在SPARQL中，它看起来像(取自此邮件列表消息):

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" )
 }

此查询在Java中的外观如何?特别是，我对模型对象的初始化方式很感兴趣.

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

推荐答案

浏览了无数页面之后，我找到了答案.也许我没有清楚地问过这个问题，但是无论如何，下面是对我有用的代码.

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();
}

我在 www的dbpedia讨论中找到了这个答案.mail-archive.com页面.

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