使用 Apache Jena 查询 DBPedia 时出错

Question

import java.sql.ResultSet;
import java.sql.SQLException;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.QueryFactory;
import com.hp.hpl.jena.query.QuerySolution;
import com.hp.hpl.jena.query.ResultSetFormatter;

public class sparq {
    public static void main (String[] args) throws SQLException
{

    String queryString=
            "PREFIX dbpedia: <http://dbpedia.org/resource/>"+
            "PREFIX category: <http://dbpedia.org/resource/Category:>"+
            "PREFIX skos: <http://www.w3.org/2004/02/skos/core#>"+
            "PREFIX dcterms: <http://purl.org/dc/terms/>"+
            "select distinct ?super where {"+
                  "?super (^skos:broader){0,4} category:Nationalist_parties, category:New_Delhi"+
                "}";



            // now creating query object

            com.hp.hpl.jena.query.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 {
                com.hp.hpl.jena.query.ResultSet results = qexec.execSelect();
                while(results.hasNext())
                {
                    QuerySolution s=results.nextSolution();
                    String strg=s.getResource("?x").toString();
                    System.out.println(strg);
                }
                //ResultSetFormatter.out(System.out, results, query);  
            }
            finally {
               qexec.close();
            }

}
}

在使用 Eclipse-Apache Jena 执行上述查询时，如果在 dbpedia sparql virtuso 的网络服务页面上触发了相同的查询，我会得到以下结果ERROR.But，它给出了所需的结果。

log4j:WARN No appenders could be found for logger (org.apache.jena.riot.system.stream.JenaIOEnvironment).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" com.hp.hpl.jena.query.QueryParseException: Encountered " "{" "{ "" at line 1, column 249.
Was expecting one of:
    <IRIref> ...
    <PNAME_NS> ...
    <PNAME_LN> ...
    <BLANK_NODE_LABEL> ...
    <VAR1> ...
    <VAR2> ...
    "true" ...
    "false" ...
    <INTEGER> ...
    <DECIMAL> ...
    <DOUBLE> ...
    <INTEGER_POSITIVE> ...
    <DECIMAL_POSITIVE> ...
    <DOUBLE_POSITIVE> ...
    <INTEGER_NEGATIVE> ...
    <DECIMAL_NEGATIVE> ...
    <DOUBLE_NEGATIVE> ...
    <STRING_LITERAL1> ...
    <STRING_LITERAL2> ...
    <STRING_LITERAL_LONG1> ...
    <STRING_LITERAL_LONG2> ...
    "(" ...
    <NIL> ...
    "[" ...
    <ANON> ...
    "+" ...
    "*" ...
    "/" ...
    "|" ...
    "?" ...

    at com.hp.hpl.jena.sparql.lang.ParserSPARQL11.perform(ParserSPARQL11.java:102)
    at com.hp.hpl.jena.sparql.lang.ParserSPARQL11.parse$(ParserSPARQL11.java:53)
    at com.hp.hpl.jena.sparql.lang.SPARQLParser.parse(SPARQLParser.java:37)
    at com.hp.hpl.jena.query.QueryFactory.parse(QueryFactory.java:148)
    at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:80)
    at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:53)
    at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:41)
    at sparq.main(sparq.java:49)

但是如果在 web.It 上使用 DBPedia Virtuso sparql 运行相同的查询，则会给出结果。 我是 Apche jena 的新手请帮忙!!!!

Answer 1

Virtuoso 接受非标准语法。 {n,m} 语法是属性路径的早期提案之一，但它没有被 SPARQL 1.1 标准接受。因此，您的查询实际上不是合法的 SPARQL 1.1（或 SPARQL 1.0）。您可以使用 sparql.org's query validator.

检查您的查询是否合法

我认为您也可以使用 Jena 的 API 要求它不首先验证查询，在这种情况下您将能够发送您的查询。例如，参见 this comment:

If you are using Jena to send a query with Virtuoso-specific features, you need to direct create a QueryEngineHTTP (which is a QueryExecution) and provide just the 2 strings, endpoint and query string. Otherwise, Jena validates the query locally but it isn't valid SPARQL hence it fails. — AndyS Sep 24 '14 at 10:48

或这个 answers.semanticweb.com 问题：jena throws QueryParsingException on correct but non-standard SPARQL。在那个问题中，OP 通过直接创建一个 QueryEngineHTTP 找到了解决方案，代码如下：

QueryEngineHTTP qe = new QueryEngineHTTP("http://dbpedia.org/sparq","select ...");
ResultSet rs = qe.execSelect();

Answer 2

我找到了问题的解决方法

void std_query()
    {
        String query = "select distinct ?super where {?super (^skos:broader){0,3} category:Nationalist_parties, category:New_Delhi}";
        QueryEngineHTTP qe = new QueryEngineHTTP("http://dbpedia.org/sparql", query);

        try {
            com.hp.hpl.jena.query.ResultSet results = qe.execSelect();
            while(results.hasNext())
            {
                QuerySolution s=results.nextSolution();
                String strg=s.getResource("?super").toString();
                System.out.println("########### Standard Sparql Result #########");
                System.out.println(strg);
            }
            //ResultSetFormatter.out(System.out, results, query);  
        }
        finally {
           qe.close();
        }
    }

使用 Apache Jena 查询 DBPedia 时出错

Error while querying DBPedia using Apache Jena

java

sparql

semantic-web

dbpedia

apache-jena