Java Jena SPARQL 查询未检索到结果

Question

我正在尝试在 Java 中使用 Jena 来运行 SPARQL 查询并从 .ttl 文件中检索结果。由于某种原因，未检索到所需的结果。我查看了我的 SPARQL 查询，我不确定错误在哪里，但没有结果被传送到我的 ResultSet 对象。下面是我的代码：

BasicConfigurator.configure();
FileManager.get().addLocatorClassLoader(QuerySparql.class.getClassLoader());
Model model = FileManager.get().loadModel(My_Path//sample.ttl", "TTL");
String queryString = 
            "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>\n" +
            "PREFIX foaf: <http://xmlns.com/foaf/0.1/name>\n" +
            "PREFIX dbo: <http://dbpedia.org/ontology/>\n" +
            "PREFIX db: <http://dbpedia.org/resource/>\n " +
            "SELECT ?team WHERE { \n" + 
            "?simeon foaf:name \"Simeon Ikudabo\"@en .\n" +
            "?simeon dbo:team ?team\n" +
            "}";
Query query = QueryFactory.create(queryString);
QueryExecution qexec = QueryExecutionFactory.create(query, model);
try {
        ResultSet results = qexec.execSelect();
        while(results.hasNext()) {
            QuerySolution soln = results.nextSolution();
            Literal team = soln.getLiteral("team");
            System.out.println(team);
        }
    }
catch(Exception e) {
        e.printStackTrace(System.out);
}

System.out.println("Done");

这是控制台中的输出，但它实际上并没有获取我正在寻找的任何结果，而是完全跳过了 while 循环，因为 ResultSet 中没有结果：

3 [main] DEBUG Jena  - Jena initialization
375 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorFile
377 [main] DEBUG org.apache.jena.util.FileManager  - Add location: ClassLoaderLocator
384 [main] DEBUG org.apache.jena.util.LocationMapper  - Failed to find configuration: file:location-mapping.rdf;file:location-mapping.n3;file:location-mapping.ttl;file:etc/location-mapping.rdf;file:etc/location-mapping.n3;file:etc/location-mapping.ttl
384 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorFile
395 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorURL
395 [main] DEBUG org.apache.jena.util.FileManager  - Add location: ClassLoaderLocator
423 [main] DEBUG org.apache.jena.riot.system.stream.JenaIOEnvironment  - Failed to find configuration: location-mapping.ttl;location-mapping.rdf;location-mapping.n3;etc/location-mapping.rdf;etc/location-mapping.n3;etc/location-mapping.ttl
1731 [main] DEBUG org.apache.jena.info  - System architecture: 64 bit
1862 [main] DEBUG org.apache.jena.info  - System architecture: 64 bit
1896 [main] DEBUG org.apache.jena.util.FileManager  - loadModel(My_Path//sample.ttl, TTL)
1897 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - Not mapped: My_Path//sample.ttl
1951 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - Found: My_Path//sample.ttl (LocatorFile)
2633 [main] DEBUG org.apache.jena.shared.LockMRSW  - Lock : main
2638 [main] DEBUG org.apache.jena.shared.LockMRSW  - Lock : main
Done

如您所见，我在本地 dbpedia turtle 文件中创建了变量 ?team，它是一个 dbpedia.org/ontology/team。本例中的 ?simeon 是正在查找的运动员，而 Simeon 将反映 foaf:name "Simeon Ikudabo"@en。我的最后一个三重声明是 ?simeon dbo:team ?team。这应该找到与 Simeon Ikudabo 相对应的 dbpedia ontology 团队值。然而，出于某种原因，ResultSet 不会检索此值。我在网上查看了我的查询可能有什么问题，但我不确定我的研究可能是什么问题。这是我的包含数据的 .ttl 文件，看起来格式正确：

<http://dbpedia.org/resource/Simeon_Ikudabo> <http://dbpedia.org/ontology/team> 
<http://dbpedia.org/resource/Indiana_Hoosiers> .
<http://dbpedia.org/resource/Simeon_Ikudabo> <http://www.xmlns.com/foaf/0.1/name> "Simeon Ikudabo"@en .
<http://dbpedia.org/resource/Nick_Mangeri> <http://dbpedia.org/ontology/team> <http://dbpedia.org/resource/Akron_Zips> .
<http://dbepdia.org/resource/Nick_Mangeri> <http://www.xmlns.com/foaf/0.1/name> "Nick Mangeri"@en .

我也考虑到了 IO 问题的可能性，但是当我只是阅读 Java 中的模型时，它似乎从文件中获取了正确的 IO。这是我简单阅读模型的代码：

Model model = ModelFactory.createDefaultModel();
model.read("My_Path//sample.ttl", "TURTLE");
model.write(System.out);

这是输出：

0 [main] DEBUG Jena  - Jena initialization
417 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorFile
419 [main] DEBUG org.apache.jena.util.FileManager  - Add location: ClassLoaderLocator
428 [main] DEBUG org.apache.jena.util.LocationMapper  - Failed to find configuration: file:location-mapping.rdf;file:location-mapping.n3;file:location-mapping.ttl;file:etc/location-mapping.rdf;file:etc/location-mapping.n3;file:etc/location-mapping.ttl
428 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorFile
431 [main] DEBUG org.apache.jena.util.FileManager  - Add location: LocatorURL
431 [main] DEBUG org.apache.jena.util.FileManager  - Add location: ClassLoaderLocator
457 [main] DEBUG org.apache.jena.riot.system.stream.JenaIOEnvironment  - Failed to find configuration: location-mapping.ttl;location-mapping.rdf;location-mapping.n3;etc/location-mapping.rdf;etc/location-mapping.n3;etc/location-mapping.ttl
1793 [main] DEBUG org.apache.jena.info  - System architecture: 64 bit
1912 [main] DEBUG org.apache.jena.info  - System architecture: 64 bit
2254 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - Not mapped: My_Path//sample.ttl
2255 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - open(My_Path//sample.ttl)
2255 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - Not mapped: My_Path//sample.ttl
2288 [main] DEBUG org.apache.jena.riot.system.stream.StreamManager  - Found: My_Path//sample.ttl (LocatorFile)
<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:j.0="http://dbpedia.org/ontology/"
    xmlns:j.1="http://dbpedia.org/ontology/"
    xmlns:j.2="http://www.xmlns.com/foaf/0.1/">
<rdf:Description rdf:about="http://dbpedia.org/resource/Nick_Mangeri">
    <j.1:team rdf:resource="http://dbpedia.org/resource/Akron_Zips"/>
</rdf:Description>
<rdf:Description rdf:about="http://dbepdia.org/resource/Nick_Mangeri">
    <j.2:name xml:lang="en">Nick Mangeri</j.2:name>
</rdf:Description>
<rdf:Description rdf:about="http://dbpedia.org/resource/Simeon_Ikudabo">
    <j.2:name xml:lang="en">Simeon Ikudabo</j.2:name>
    <j.0:team rdf:resource="http://dbpedia.org/resource/Indiana_Hoosiers"/>
 </rdf:Description>
</rdf:RDF>

所以我知道 Jena 可以读取该文件。我使用 Virtuoso SPARQL 端点为 DBpedia 创建了一个 SIMILAR 查询，并始终获得正确的结果。他是一个类似的查询，我运行作为来自 DBpedia 的 Virtuoso SPARQL 端点的测试：

prefix dbpedia-owl: <http://dbpedia.org/ontology/>
prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>
prefix db: <http://dbpedia.org/resource/>

SELECT ?draftTeam WHERE{
?kobe dbpedia-owl:draftTeam ?draftTeam .
?kobe foaf:name "Kobe Bryant"@en .
}

我知道 Virtuoso SPARQL 端点与 Apache Jena SPARQL 查询略有不同，但通用语法相同。我很困惑为什么我不能在耶拿执行查询。

Answer 1

你的数据有三倍

<http://dbpedia.org/resource/Simeon_Ikudabo> <http://dbepdia.org/ontology/team> <http://dbpedia.org/resource/Indiana_Hoosiers> .

还有一个错字：dbepdia 而不是属性中的 dbpedia。当我在打印模型中注意到有两个名称空间时，我发现了这一点：

xmlns:j.0="http://dbepdia.org/ontology/"
xmlns:j.1="http://dbpedia.org/ontology/"

Answer 2

我能够解决问题。这是下面的代码示例：

BasicConfigurator.configure();
FileManager.get().addLocatorClassLoader(QuerySparql.class.getClassLoader());
Model model = FileManager.get().loadModel("My_Path//sample.ttl", "TTL");
String queryString = 
            "PREFIX db: <http://dbpedia.org/resource> \n" +
            "SELECT ?meshId WHERE{ \n" + 
            "?autism <http://xmlns.com/foaf/0.1/name> \"Autism\"@en .\n" +
            "?autism <http://dbpedia.org/ontology/meshId> ?meshId \n" +
            "}";

Query query = QueryFactory.create(queryString);
QueryExecution qexec = QueryExecutionFactory.create(query, model);

ResultSet results = qexec.execSelect();
if(results.hasNext()) {
    System.out.println("has results!");
}
else {
    System.out.println("No Results!");
}

while(results.hasNext()) {
    QuerySolution soln = results.nextSolution();
    Literal r = soln.getLiteral("meshId");
    System.out.println(r);
}

错误似乎在查询中。我需要使用 dbpedia 文件中的完整 URL 来进行查询。在 dbpedia 文件中，url 看起来像这样：

<http://xmlns.com/foaf/0.1/name> "Autism"@en .

在实际查询中使用 URL，如下所示：

"?autism <http://xmlns.com/foaf/0.1/name> \"Autism\"@en .\n

最终解决了问题。我之前在查询中使用的前缀与 dbpedia 文件中的前缀不直接匹配。所以前缀：

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

将不起作用。相反，我需要放置与 dbpedia 文件中找到的直接匹配的 URL。

Java Jena SPARQL 查询未检索到结果

Java Jena SPARQL Query not retrieving results

java

sparql

jena

dbpedia