基于谓词节点检索特定RDF图三元组

我使用dotnetrdf发送Sparql

构造

查询并计算结果

首先，我试图找到表示给定类型的个体的所有Uri节点，比如

http://www.example.com/InterestingThing

因此，我想使用，传递

http://www.w3.org/1999/02/22-rdf-syntax-ns#type

作为谓词和

http://www.example.com/InterestingThing

作为一个对象。该方法需要两个对象来实现，因此我尝试使用图的

问题：找不到谓词。 在调试器中查看

IGraph

对象时，似乎

GetUriNode

只能找到图形中包含的内容，并且只包含用作主题或对象的Uri节点，但没有用作谓词的Uri节点

现在，谓词Uri节点显然就在那里——我在探索图的结构时可以看到它们。它们出现在中，可以直接从该对象检索，也可以在同一对象的中找到

有趣的是，

IGraph

的一些查询方法，例如or确实有重载，只接受一个而不是一个-但不接受

现在，各种可能的解决办法显而易见：

• 使用只接受一个

  Uri

  实例的

  GetTriplesWithPredicate

  重载，然后手动过滤生成的三元组
• 手动搜索所有三元组以获得所需的三元组
• 手动搜索

  谓词节点列表

  ，并找到具有已搜索URI的节点

不过，所有这些看起来都不必要地麻烦，因为现有的方法乍一看就表明，应该能够使用

GetUriNode

检索两个节点，然后将它们传递给一个现成的查询方法，例如

GetTriplesWithObjectPredicate

因此，我的问题是：

我是否遗漏了dotnetrdf库中或概念上RDF中的任何内容，或者这种行为是否会给开发人员带来设计上的障碍？

下面是一个C#测试用例来重现问题（查询DBpedia）：

使用系统；
使用System.Collections.Generic；
使用System.Linq；
使用VDS.RDF；
使用VDS.RDF.Query；
名称空间测试
{
班级计划
{
公共静态void Main（字符串[]args）
{
//质疑
//所有要分析的条目都声明为属于临时类型，并且
//两个属性映射到临时属性标识符。
Console.WriteLine（）；
var endpoint=new SparqlRemoteEndpoint（新Uri（“http://dbpedia.org/sparql"));
string query=“前缀dbpedia owl:\n”
+“前缀ex:\n”
+“\n”
+“构造{\n”
+“？r a ex:记录。\n”
+“？r ex:prop1？v1。\n”
+“？r ex:prop2？v2。\n”
+“}\n”
+“其中{\n”
+“{\n”
+“选择？r\n”
+“其中{\n”
+“？r a dbpedia owl:工作。\n”
+“筛选器（存在{r dbpedia owl:originalLanguage[]}&&EXISTS{r dbpedia owl:author/dbpedia owl:birthPlace[]}）。\n”
+“}限制5\n”
+“}\n”
+“？r dbpedia owl:原始语言？v1。\n”
+“？r dbpedia owl:作者/dbpedia owl:出生地？v2。\n”
+ "}";
Console.WriteLine（查询）；
Console.WriteLine（）；
IGraph graph=endpoint.QueryWithResultGraph（查询）；
PrintNodes（“IGraph.Nodes”，graph.Nodes）；
Console.WriteLine（“来自IGraph.triples:”）的所有三元组；
foreach（图中的变量三元组。三元组）{
Console.WriteLine（“-S:+NodeToString（triple.Subject））；
WriteLine（“P:+NodeToString（triple.Predicate））；
WriteLine（“O:+NodeToString（triple.Object））；
}
Console.WriteLine（）；
PrintNodes（“IGraph.Triples.SubjectNodes”，graph.Triples.SubjectNodes）；
PrintNodes（“IGraph.Triples.PredicateNodes”，graph.Triples.PredicateNodes）；
PrintNodes（“IGraph.Triples.ObjectNodes”，graph.Triples.ObjectNodes）；
//图形分析
//下面的代码尝试准确地检索临时文件的项
//键入“记录”。
var typeNode=TryFindUriNode（图形，新Uri（NamespaceMapper.RDF+“类型”）；
var recordNode=TryFindUriNode（图形，新Uri（“http://www.example.com/record"));
Console.WriteLine（）；
TryFindAllNodes（“subjects”，graph，graph.Triples.SubjectNodes.OfType（）.Select（node=>node.Uri））；
TryFindAllNodes（“谓词”，graph，graph.Triples.PredicateNodes.OfType（）.Select（node=>node.Uri））；
TryFindAllNodes（“objects”、graph、graph.Triples.ObjectNodes.OfType（）.Select（node=>node.Uri））；
Console.WriteLine（）；
var createdTypeNode=graph.CreateUriNode（新Uri（NamespaceMapper.RDF+“类型”）；
var createdRecordNode=graph.CreateUriNode（新Uri（“http://www.example.com/record"));
if（（typeNode！=null）&&（recordNode！=null））{
WriteLine（“{0}个三元组，具有找到的谓词和找到的对象。”，
graph.GetTriplesWithPredicateObject（typeNode，recordNode.Count（））；
}
if（typeNode！=null）{
WriteLine（“{0}个三元组，具有找到的谓词和创建的对象。”，
graph.GetTriplesWithPredicateObject（typeNode，createdRecordNode.Count（））；
}
if（recordNode！=null）{
Console.WriteLine（“{0}个三元组），创建了pred
PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>
PREFIX ex: <http://www.example.com/>

CONSTRUCT {
  ?r a ex:record.
  ?r ex:prop1 ?v1.
  ?r ex:prop2 ?v2.
}
WHERE {
  {
    SELECT ?r
    WHERE {
      ?r a dbpedia-owl:Work.
      FILTER(EXISTS { ?r dbpedia-owl:originalLanguage [] } && EXISTS { ?r dbpedia-owl:author/dbpedia-owl:birthPlace [] }).
    } LIMIT 5
  }
  ?r dbpedia-owl:originalLanguage ?v1.
  ?r dbpedia-owl:author/dbpedia-owl:birthPlace ?v2.
}

IGraph.Nodes:
- http://dbpedia.org/resource/Electra_(Sophocles) (UriNode)
- http://dbpedia.org/resource/Peer_Gynt (UriNode)
- http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
- http://dbpedia.org/resource/The_Field (UriNode)
- http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)
- http://www.example.com/record (UriNode)
- http://dbpedia.org/resource/Ancient_Greek (UriNode)
- http://dbpedia.org/resource/Colonus (UriNode)
- http://dbpedia.org/resource/Norwegian_language (UriNode)
- http://dbpedia.org/resource/Skien (UriNode)
- http://dbpedia.org/resource/Norway (UriNode)
- http://dbpedia.org/resource/Czech_language (UriNode)
- http://dbpedia.org/resource/Kingdom_of_Bohemia (UriNode)
- http://dbpedia.org/resource/Bohemia (UriNode)
- http://dbpedia.org/resource/Mal%C3%A9_Svato%C5%88ovice (UriNode)
- http://dbpedia.org/resource/Austria-Hungary (UriNode)
- http://dbpedia.org/resource/English_language (UriNode)
- http://dbpedia.org/resource/Irish_Free_State (UriNode)
- http://dbpedia.org/resource/Listowel (UriNode)
- http://dbpedia.org/resource/County_Kerry (UriNode)

All triples from IGraph.Triples:
- S: http://dbpedia.org/resource/Electra_(Sophocles) (UriNode)
  P: http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
  O: http://www.example.com/record (UriNode)
- S: http://dbpedia.org/resource/Electra_(Sophocles) (UriNode)
  P: http://www.example.com/prop1 (UriNode)
  O: http://dbpedia.org/resource/Ancient_Greek (UriNode)
- S: http://dbpedia.org/resource/Electra_(Sophocles) (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Colonus (UriNode)
- S: http://dbpedia.org/resource/Peer_Gynt (UriNode)
  P: http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
  O: http://www.example.com/record (UriNode)
- S: http://dbpedia.org/resource/Peer_Gynt (UriNode)
  P: http://www.example.com/prop1 (UriNode)
  O: http://dbpedia.org/resource/Norwegian_language (UriNode)
- S: http://dbpedia.org/resource/Peer_Gynt (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Skien (UriNode)
- S: http://dbpedia.org/resource/Peer_Gynt (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Norway (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
  O: http://www.example.com/record (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.example.com/prop1 (UriNode)
  O: http://dbpedia.org/resource/Czech_language (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Kingdom_of_Bohemia (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Bohemia (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Mal%C3%A9_Svato%C5%88ovice (UriNode)
- S: http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Austria-Hungary (UriNode)
- S: http://dbpedia.org/resource/The_Field (UriNode)
  P: http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
  O: http://www.example.com/record (UriNode)
- S: http://dbpedia.org/resource/The_Field (UriNode)
  P: http://www.example.com/prop1 (UriNode)
  O: http://dbpedia.org/resource/English_language (UriNode)
- S: http://dbpedia.org/resource/The_Field (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Irish_Free_State (UriNode)
- S: http://dbpedia.org/resource/The_Field (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Listowel (UriNode)
- S: http://dbpedia.org/resource/The_Field (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/County_Kerry (UriNode)
- S: http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)
  P: http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
  O: http://www.example.com/record (UriNode)
- S: http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)
  P: http://www.example.com/prop1 (UriNode)
  O: http://dbpedia.org/resource/Norwegian_language (UriNode)
- S: http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Skien (UriNode)
- S: http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)
  P: http://www.example.com/prop2 (UriNode)
  O: http://dbpedia.org/resource/Norway (UriNode)

IGraph.Triples.SubjectNodes:
- http://dbpedia.org/resource/Electra_(Sophocles) (UriNode)
- http://dbpedia.org/resource/Peer_Gynt (UriNode)
- http://dbpedia.org/resource/Pictures_from_the_Insects'_Life (UriNode)
- http://dbpedia.org/resource/The_Field (UriNode)
- http://dbpedia.org/resource/The_Lady_from_the_Sea (UriNode)

IGraph.Triples.PredicateNodes:
- http://www.w3.org/1999/02/22-rdf-syntax-ns#type (UriNode)
- http://www.example.com/prop1 (UriNode)
- http://www.example.com/prop2 (UriNode)

IGraph.Triples.ObjectNodes:
- http://www.example.com/record (UriNode)
- http://dbpedia.org/resource/Ancient_Greek (UriNode)
- http://dbpedia.org/resource/Colonus (UriNode)
- http://dbpedia.org/resource/Norwegian_language (UriNode)
- http://dbpedia.org/resource/Skien (UriNode)
- http://dbpedia.org/resource/Norway (UriNode)
- http://dbpedia.org/resource/Czech_language (UriNode)
- http://dbpedia.org/resource/Kingdom_of_Bohemia (UriNode)
- http://dbpedia.org/resource/Bohemia (UriNode)
- http://dbpedia.org/resource/Mal%C3%A9_Svato%C5%88ovice (UriNode)
- http://dbpedia.org/resource/Austria-Hungary (UriNode)
- http://dbpedia.org/resource/English_language (UriNode)
- http://dbpedia.org/resource/Irish_Free_State (UriNode)
- http://dbpedia.org/resource/Listowel (UriNode)
- http://dbpedia.org/resource/County_Kerry (UriNode)

Trying to find all subjects:
http://dbpedia.org/resource/Electra_(Sophocles) WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Peer_Gynt WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Pictures_from_the_Insects'_Life WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/The_Field WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/The_Lady_from_the_Sea WAS found by IGraph.GetUriNode.
Trying to find all predicates:
http://www.w3.org/1999/02/22-rdf-syntax-ns#type was NOT found by IGraph.GetUriNode.
http://www.example.com/prop1 was NOT found by IGraph.GetUriNode.
http://www.example.com/prop2 was NOT found by IGraph.GetUriNode.
Trying to find all objects:
http://www.example.com/record WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Ancient_Greek WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Colonus WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Norwegian_language WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Skien WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Norway WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Czech_language WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Kingdom_of_Bohemia WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Bohemia WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Mal‚_Svatonovice WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Austria-Hungary WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/English_language WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Irish_Free_State WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/Listowel WAS found by IGraph.GetUriNode.
http://dbpedia.org/resource/County_Kerry WAS found by IGraph.GetUriNode.

http://www.w3.org/1999/02/22-rdf-syntax-ns#type was NOT found by IGraph.GetUriNode.
http://www.example.com/record WAS found by IGraph.GetUriNode.
5 triple(s) with created predicate and found object.
5 triple(s) with created predicate and created object.