我对使用Java代码的SPARQL端点有问题。

特别是，我有这个Java类：

public class example {

public static void main(String[] args) {

String value = "http://dbpedia.org/resource/Fred_Guy";

example exam = example();

QueryExecution qe = exam.query(value);

ResultSet results = ResultSetFactory.copyResults( qe.execSelect() );

}

public QueryExecution query(String stringa){

ParameterizedSparqlString qs = new ParameterizedSparqlString( "" +

"prefix dbpediaont: \n" +

"prefix rdf: \n" +

"\n" +

"select ?resource where {\n" +

"?mat rdf:type ?resource\n" +

"filter strstarts(str(?resource), dbpediaont:)\n" +

"}" );

Resource risorsa = ResourceFactory.createResource(stringa);

qs.setParam( "mat", risorsa );

QueryExecution exec = QueryExecutionFactory.sparqlService( "http://dbpedia.org/sparql", qs.asQuery() );

ResultSet results = ResultSetFactory.copyResults( exec.execSelect() );

while ( results.hasNext() ) {

System.out.println( results.next().get( "resource" ));

}

// A simpler way of printing the results.

ResultSetFormatter.out( results );

return exec;

}

}

我想检索谓词为“ RDF：type” 的资源“

http://dbpedia.org/resource/Fred_Guy ”

的对象。但是我有一个我不明白的错误：

Exception in thread "main" HttpException: 500

at com.hp.hpl.jena.sparql.engine.http.HttpQuery.execGet(HttpQuery.java:340)

at com.hp.hpl.jena.sparql.engine.http.HttpQuery.exec(HttpQuery.java:276)

at com.hp.hpl.jena.sparql.engine.http.QueryEngineHTTP.execSelect(QueryEngineHTTP.java:345)

at MyPackage.example.main(example.java:19)

为什么会出现此错误？

我正在尝试执行此查询

没有写strstarts，我得到这个错误：

Virtuoso 37000 Error SP031: SPARQL compiler: No one quad map pattern is suitable for GRAPH { "http://dbpedia.org/resource/Fred_Guy" ?resource } triple at line 7

SPARQL query:

define sql:big-data-const 0

#output-format:text/html

define sql:signal-void-variables 1 define input:default-graph-uri prefix dbpediaont:

prefix rdf:

select ?resource where {

"http://dbpedia.org/resource/Fred_Guy" rdf:type ?resource

}

我在这里做错了什么？

我试图用Virtuoso编写以下代码：

prefix dbpediaont:

prefix rdf:

select ?resource where {

dbpedia:Fred_Guy rdf:type ?resource

}

如何用耶拿代码编写？