以下查询在对以下数据运行时,应显示" foaf:name"从数据,但它没有显示任何东西。查询有问题吗?
PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX foaf:<http://www.xmlns.com/foaf/0.1>
select * where {
?person foaf:name ?x .
}
import com.hp.hpl.jena.query.Query;
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.ResultSet;
import com.hp.hpl.jena.rdf.model.Literal;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.util.FileManager;
public class Sparql {
public static void main(String[] args) {
sparqlTest();
}
static void sparqlTest()
{
FileManager.get().addLocatorClassLoader(Sparql.class.getClassLoader());
Model model=FileManager.get().loadModel("C:/dataTest.rdf");
String queryString="PREFIX rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>"+
"PREFIX foaf:<http://www.xmlns.com/foaf/0.1>"+
"select * where {"+
"?person foaf:name ?x ."+
"}";
Query query=QueryFactory.create(queryString);
QueryExecution qexec=QueryExecutionFactory.create(query,model);
try{
ResultSet results=qexec.execSelect();
while(results.hasNext() )
{
QuerySolution soln=results.nextSolution();
Literal name=soln.getLiteral("x");
System.out.println(name);
}
}
finally{
qexec.close();
}
}
}
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:foaf="http://xmlns.com/foaf/0.1/"
xmlns:admin="http://webns.net/mvcb/"
xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
<foaf:PersonalProfileDocument rdf:about="">
<foaf:maker>
<foaf:Person rdf:about="#me">
<foaf:mbox_sha1sum>b01b5835fa8ae7b7582968a7ecacb9b85503a6c9</foaf:mbox_sha1sum>
<foaf:phone rdf:resource="tel:12345"/>
<foaf:givenname>George</foaf:givenname>
<foaf:workInfoHomepage rdf:resource="urn:development"/>
<foaf:title>Dr.</foaf:title>
<foaf:name>George V</foaf:name>
<foaf:homepage rdf:resource="urn:betacoding.net"/>
<foaf:workplaceHomepage rdf:resource="urn:work"/>
<foaf:knows>
<foaf:Person>
<foaf:name>Charlie</foaf:name>
<foaf:mbox_sha1sum>27f94c268f1a1c6004be361f4045d43c3745c0de</foaf:mbox_sha1sum>
</foaf:Person>
</foaf:knows>
<foaf:schoolHomepage rdf:resource="urn: a school"/>
<foaf:family_name>V</foaf:family_name>
<foaf:nick>Jorch</foaf:nick>
</foaf:Person>
</foaf:maker>
<foaf:primaryTopic rdf:resource="#me"/>
<admin:generatorAgent rdf:resource="http://www.ldodds.com/foaf/foaf-a-matic"/>
<admin:errorReportsTo rdf:resource="mailto:leigh@ldodds.com"/>
</foaf:PersonalProfileDocument>
</rdf:RDF>
答案 0 :(得分:3)
查询中的前缀错误。
http://www.xmlns.com/foaf/0.1
这意味着当您在查询中使用 foaf:name 时,它会扩展为
http://www.xmlns.com/foaf/0.1name
然而,在数据中,foaf前缀是
http://xmlns.com/foaf/0.1/
以便 foaf:name 是
http://xmlns.com/foaf/0.1/name
也就是说,您需要添加最终斜杠,并且需要删除最初的www
。因此,您最终得到一个查询和结果如下:
prefix foaf: <http://xmlns.com/foaf/0.1/>
select * where {
?s foaf:name ?o .
}
------------------------------
| s | o |
==============================
| _:b0 | "Charlie" |
| <data.rdf#me> | "George V" |
------------------------------
请注意,数据未指定任何xml:base。由于文档在<#me> foaf:name "George V"
中使用了主题的相对URI,因此您可能会看到与我在结果中显示的主题不同的URI。