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，未检索所需的结果。我已经查看了我的SPARQL查询，但不确定错误在哪里，但没有结果传递给我的ResultSet对象。这是我下面的代码：
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 ?teamn" +
"}";
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并完全跳过 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，我创建了变量?team，这是我本地 dbpedia 龟文件中的一个dbpedia.org/ontology/team。 在这个例子中?simeon是正在查找的运动员，Simeon 将反映foaf:name "Simeon Ikudabo"@en。我最后的三重陈述是?simeon dbo:team ?team.这应该找到与Simeon Ikudabo对应的dbpedia本体团队值。但是，由于某种原因，ResultSet不会检索此值。我已经在网上查看了我的查询可能出现的问题，但我不确定我的研究中可能出现的问题是什么。这是我.ttl包含数据的文件，它似乎格式正确：
<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 .
我还考虑了 IO 问题的可能性，但是当我简单地在 Java 中读取模型时，它似乎从文件中获得了正确的 IO。这是我用于简单读取模型的代码：
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>
所以我知道耶拿可以读取文件。我使用 DBpedia 的 Virtuoso SPARQL 端点创建了一个类似的查询，并始终如一地获得正确的结果。他是一个类似的查询，我从 DBpedia 的 Virtuoso SPARQL 端点运行作为测试：
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，但它是相同的一般语法。我很困惑为什么我不能在耶拿执行查询。
我能够解决这个问题。下面是以下代码的示例：
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 进行查询。在 dbpedia 文件中，url 如下所示：
<http://xmlns.com/foaf/0.1/name> "Autism"@en .
在实际查询中使用该 URL，如下所示：
"?autism <http://xmlns.com/foaf/0.1/name> "Autism"@en .n
最终解决了这个问题。我之前在查询中使用的前缀与 dbpedia 文件中的前缀没有直接匹配。所以前缀：
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
行不通。相反，我需要放置与 dbpedia 文件中找到的 URL 直接匹配的 URL。
您的数据具有三元组
<http://dbpedia.org/resource/Simeon_Ikudabo> <http://dbepdia.org/ontology/team> <http://dbpedia.org/resource/Indiana_Hoosiers> .
还有一个错别字：dbepdia而不是dbpedia。当我在打印模型中注意到有两个命名空间时，我发现了这一点：
xmlns:j.0="http://dbepdia.org/ontology/"
xmlns:j.1="http://dbpedia.org/ontology/"