从耶拿模型中检索项目
[英]Retrieve items from a model in jena
问题描述
I am running a query and saving the result into a JSON file. 
我正在运行查询并将结果保存到JSON文件中。 I am loading the json file as a model and trying to retrieve the list of subjects, objects and predicates. 我正在将json文件作为模型加载，并尝试检索主题，对象和谓词的列表。 However I am getting the following error: 但是我收到以下错误：
Exception in thread "main" org.apache.jena.riot.RiotException: [line: 2, col: 3 ] Relative IRI: head at org.apache.jena.riot.system.ErrorHandlerFactory$ErrorHandlerStd.error(ErrorHandlerFactory.java:128) at org.apache.jena.riot.checker.CheckerIRI.iriViolations(CheckerIRI.java:138) at org.apache.jena.riot.checker.CheckerIRI.iriViolations(CheckerIRI.java:100) at org.apache.jena.riot.system.ParserProfileChecker.makeIRI(ParserProfileChecker.java:66) at org.apache.jena.riot.system.ParserProfileChecker.resolveIRI(ParserProfileChecker.java:59) at org.apache.jena.riot.system.ParserProfileChecker.createURI(ParserProfileChecker.java:112) at org.apache.jena.riot.lang.LangRDFJSON.tryParseTriples(LangRDFJSON.java:121) at org.apache.jena.riot.lang.LangRDFJSON.tryParseGraph(LangRDFJSON.java:68) at org.apache.jena.riot.lang.LangRDFJSON.runParser(LangRDFJSON.java:56) at org.apache.jena.riot.lang.LangBase.parse(LangBase.java:42) at org.apache.jena.riot.RDFParserRegistry$ReaderRIOTLang.read(RDFParserRegi
My code is: 我的代码是：
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStream;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryExecution;
import org.apache.jena.query.QueryExecutionFactory;
import org.apache.jena.query.QueryFactory;
import org.apache.jena.query.QuerySolution;
import org.apache.jena.query.ResultSet;
import org.apache.jena.query.ResultSetFormatter;
import org.apache.jena.rdf.model.Literal;
import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.RDFNode;
import org.apache.jena.rdf.model.Resource;
import org.apache.jena.rdf.model.Statement;
import org.apache.jena.rdf.model.StmtIterator;
import org.apache.jena.util.FileManager;
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
String queryString = "PREFIX owl: <http://www.w3.org/2002/07/owl#>"
+ "PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>"
+ "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>"
+ "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>"
+ "PREFIX foaf: <http://xmlns.com/foaf/0.1/>" + "PREFIX dc: <http://purl.org/dc/elements/1.1/>"
+ "PREFIX dbr: <http://dbpedia.org/resource/>" + "PREFIX dbpedia2: <http://dbpedia.org/property/>"
+ "PREFIX dbpedia: <http://dbpedia.org/>" + "PREFIX skos: <http://www.w3.org/2004/02/skos/core#>"
+ "PREFIX dbo: <http://dbpedia.org/ontology/>" + "select distinct ?p ?o where {"
+ "dbr:Cristiano_Ronaldo ?p ?o " + "filter(langMatches(lang(?o),'en'))" +
"}";
Query query = QueryFactory.create(queryString);
QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query);
ResultSet results = qexec.execSelect();
FileOutputStream oFile;
try {
oFile = new FileOutputStream("output4.json", false);
ResultSetFormatter.outputAsJSON(oFile, results);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
qexec.close();
FileManager.get().addLocatorClassLoader(Main.class.getClassLoader());
Model model = FileManager.get().loadModel("output4.json", null, "RDF/JSON");
StmtIterator iter = model.listStatements();
try {
while (iter.hasNext()) {
Statement stmt = iter.next();
Resource s = stmt.getSubject();
Resource p = stmt.getPredicate();
RDFNode o = stmt.getObject();
System.out.println(s.toString());
System.out.println(p.toString());
System.out.println(o.toString());
}
} finally {
if (iter != null)
iter.close();
}
}
}
As per AKSW suggestion I have tried it with the construct query: 根据AKSW的建议，我已经尝试使用构造查询：
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryExecution;
import org.apache.jena.query.QueryExecutionFactory;
import org.apache.jena.query.QueryFactory;
import org.apache.jena.query.ResultSetFactory;
import org.apache.jena.query.ResultSetFormatter;
import org.apache.jena.query.ResultSetRewindable;
import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.RDFNode;
import org.apache.jena.rdf.model.Resource;
import org.apache.jena.rdf.model.Statement;
import org.apache.jena.rdf.model.StmtIterator;
import org.apache.jena.util.FileManager;
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
String queryString = "PREFIX owl: <http://www.w3.org/2002/07/owl#>"
+ "PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>"
+ "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>"
+ "PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>"
+ "PREFIX foaf: <http://xmlns.com/foaf/0.1/>" + "PREFIX dc: <http://purl.org/dc/elements/1.1/>"
+ "PREFIX dbr: <http://dbpedia.org/resource/>" + "PREFIX dbpedia2: <http://dbpedia.org/property/>"
+ "PREFIX dbpedia: <http://dbpedia.org/>" + "PREFIX skos: <http://www.w3.org/2004/02/skos/core#>"
+ "PREFIX dbo: <http://dbpedia.org/ontology/>" + "select distinct ?p ?o where {"
+ "dbr:Cristiano_Ronaldo ?p ?o " + "filter(langMatches(lang(?o),'en'))" +
"}";
Query query = QueryFactory.create(queryString);
QueryExecution qexec = QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql", query);
FileOutputStream oFile;
try {
oFile = new FileOutputStream("output4.ttl", false);
Model result21 = qexec.execConstruct();
result21.write(oFile, "TURTLE");
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
qexec.close();
FileManager.get().addLocatorClassLoader(Main.class.getClassLoader());
Model model = FileManager.get().loadModel("output4.ttl", null, "TURTLE");
StmtIterator iter = model.listStatements();
try {
while (iter.hasNext()) {
Statement stmt = iter.next();
Resource s = stmt.getSubject();
Resource p = stmt.getPredicate();
RDFNode o = stmt.getObject();
System.out.println(s.toString());
System.out.println(p.toString());
System.out.println(o.toString());
}
} finally {
if (iter != null)
iter.close();
}
}
}
The printed results are weird and doesn't provide the subjects, objects and predicates properly. 打印的结果很奇怪，不能正确提供主题，宾语和谓词。 Below is the response printed in the console: result 以下是控制台中打印的响应： 结果
1 个解决方案
解决方案1
0 已采纳 2016-07-31 11:49:49
The problem is that you're running a SELECT query which gives you back a resultset. 问题是您正在运行SELECT查询，该查询将为您提供结果集。 This resultset does not represent the RDF triples as you probably expect. 该结果集并不代表您可能期望的RDF三元组。 Especially since you only select p and o , thus, the subject would be missing. 特别是由于仅选择p和o ，因此将丢失主题。 Then you save that resultset as JSON, see https://www.w3.org/TR/rdf-sparql-json-res/ for a description of the format. 然后将该结果集另存为JSON，有关格式的说明，请参见https://www.w3.org/TR/rdf-sparql-json-res/ 。 As a consequence, there are no triples in the JSON file that you can load into a JENA model back. 因此，JSON文件中没有三元组，您可以将其加载回JENA模型。
The solution would be to use SPARQL CONSTRUCT instead. 解决方案是改用SPARQL CONSTRUCT 。 The query could be as follows: 查询可以如下：
PREFIX dbr: <http://dbpedia.org/resource/>
CONSTRUCT {
dbr:Cristiano_Ronaldo ?p ?o .
} WHERE {
dbr:Cristiano_Ronaldo ?p ?o .
FILTER(LANGMATCHES(LANG(?o),'en'))
}
In addition, you have to adapt the method call in the Jena API: 另外，您必须调整Jena API中的方法调用：
Model model = qexec.execConstruct(); // instead of execSelect();
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