-- 发布时间：8/13/2006 10:45:00 AM
-- 请问大侠：我在用SPARQL查询RDF模型时遇到的困难，求救
最近再学习SPARQL语言查询RDF时遇到很多困难，我用的是Jena接口语言如下：我使用的RDF文件内容（test.rdf）：<?xml version="1.0"?>
<rdf:RDF xmlns:rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:DC = "http://purl.org/dc/elements/1.1/"
xmlns:vCard = "http://www.w3.org/2001/vcard-rdf/3.0#"
xmlns:HongLM="http://127.0.0.1/HongLM#">
<rdf:Description rdf:about = "http://qqqfoo.com/annual-report.html" >
<DC:title> Annual Report 1999/2000 </DC:title>
<DC:creator rdf:parseType="Resource">
<vCard:FN> Corky Crystal </vCard:FN>
<vCard:N rdf:parseType="Resource">
<vCard:Family> Crystal </vCard:Family>
<vCard:Given> Corky </vCard:Given>
</vCard:N>
<vCard:EMAIL rdf:parseType="Resource">
<rdf:value> corky@qqqfoo.com </rdf:value>
<rdf:type rdf:resource="http://www.w3.org/2001/vcard-rdf/3.0#internet"/>
</vCard:EMAIL>
</DC:creator>
<DC:date> 2000-10-01 </DC:date>
<DC:subject> Company Report, Outcomes, Objectives </DC:subject>
<DC:publisher> qqqfoo.com Pty Ltd </DC:publisher>
<DC:rights> Copyright 2000 </DC:rights>
</rdf:Description>
<rdf:Description rdf:about ="http://127.0.0.1/HongLM/rt34.htm">
<HongLM:master>Jia Bao Yu</HongLM:master>
<HongLM:hasservant>Qin Wen</HongLM:hasservant>
<HongLM:haswife>Xue Bao Cha</HongLM:haswife>
</rdf:Description>
</rdf:RDF>
我用的查询模式：
"PREFIX rdfs:<http://www.w3.org/2000/01/rdf-schema#>"+
"PREFIX HongLM:<http://127.0.0.1/HongLM#>"+
"SELECT ?x ?obj " +
"WHERE {" +
"?x DC:title ?obj."
+ "}";
利用这种方法可以查询，如DC:title，DC:date，DC:subject，DC:publisher， DC:rights之类的节点，但是要查询类似，DC:creator，vCard:EMAIL这些符合节点则不能得到查询结果。
例如：
"SELECT ?x ?creator"+
"Where {"+
"?x DC:creator ?y ."+
"?y vCard:FN ??creator ."+ "}";执行的结果,不报错，无结果返回。
参考程序如下：
import java.io.InputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.*;
import com.hp.hpl.jena.query.*;
import com.hp.hpl.jena.rdf.model.*;
import com.hp.hpl.jena.ontology.OntClass;
import com.hp.hpl.jena.ontology.OntModel;
import com.hp.hpl.jena.rdf.model.ModelFactory;
import com.hp.hpl.jena.rdf.model.Property;
import com.hp.hpl.jena.rdf.model.RDFNode;
import com.hp.hpl.jena.rdf.model.Resource;
import com.hp.hpl.jena.rdf.model.Statement;
import com.hp.hpl.jena.rdf.model.StmtIterator;
public class Rdqowl
{
public static void main(String args[])
{
// Open The RDF or OWL graph from the filesystem
try
{
InputStream in = new FileInputStream(new File("test.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();
String queryString =
"PREFIX vCard:<http://www.w3.org/2001/vcard-rdf/3.0>"+
"PREFIX DC:<http://purl.org/dc/elements/1.1/>"+
Select "?x DC:title ?title"
"WHERE {" +
"{ ?x DC:creator ?c.} "+
" OPTIONAL { ?c vCard:FN ?fname } ."+
"FILTER isBlank(?c)"
+ " }";
Query query = QueryFactory.create(queryString);
// Execute the query and obtain results
QueryExecution qe = QueryExecutionFactory.create(query, model);
ResultSet results = qe.execSelect();
// Output query results
ResultSetFormatter.out(System.out, results, query);
// Important - free up resources used running the query
qe.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}
}
}
还有一问？
用上面的方法怎么查询OWL文件？