我使用dotnetrdf发送Sparql CONSTRUCT
查询并评估结果IGraph .
首先,我试图找到代表给定类型的个体的所有Uri节点,比方说,
http://www.example.com/InterestingThing
所以,我想使用GetTriplesWithPredicateObject method,将 http://www.w3.org/1999/02/22-rdf-syntax-ns#type
作为谓词传递,将 http://www.example.com/InterestingThing
作为对象传递 . 该方法需要两个实现INode interface的对象,所以我试图用图形的GetUriNode method找到相应的节点 .
问题:未找到谓词 .
在查看调试器中的 IGraph
对象时,似乎 GetUriNode
只能找到图中Nodes enumeration中包含的内容 - 并且只包含已用作主题或对象的Uri节点,但不包含用作谓词的Uri节点 .
现在,谓词Uri节点显然在那里 - 我可以在探索图形的Triples object时看到它们 . 它们出现在Triple instances中,可以直接从该对象检索,也可以在同一对象的PredicateNodes property中找到它们 .
有趣的是, IGraph
的某些查询方法(例如GetTriplesWithObject或GetTriplesWithPredicate)确实具有接受仅仅Uri而不是INode的重载 - 但GetTriplesWithPredicateObject没有 .
现在,各种可能的解决方法是显而易见的:
-
使用仅占用
Uri
实例的GetTriplesWithPredicate
的重载,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
PredicateNodes
列表,找到搜索到Uris的列表 .
然而,所有这些似乎都是不必要的麻烦 - 因为现有的方法乍看之下,人们应该只能使用 GetUriNode
来检索两个节点,然后将这些节点传递给现成的查询方法之一,例如 GetTriplesWithObjectPredicate
.
因此,我的问题是:
Am I missing anything, either in the dotnetrdf library or conceptually, in RDF, or is this behavior with the obstacles it poses to developers by design?
这是一个重现问题的C#测试用例(查询DBpedia):
using System;
using System.Collections.Generic;
using System.Linq;
using VDS.RDF;
using VDS.RDF.Query;
namespace Test
{
class Program
{
public static void Main(string[] args)
{
// Querying
// All entries to analyze are declared to belong to a temporary type, and
// two properties are mapped to temporary property identifiers.
Console.WriteLine();
var endpoint = new SparqlRemoteEndpoint(new Uri("http://dbpedia.org/sparql"));
string query = "PREFIX dbpedia-owl: <http://dbpedia.org/ontology/>\n"
+ "PREFIX ex: <http://www.example.com/>\n"
+ "\n"
+ "CONSTRUCT {\n"
+ " ?r a ex:record.\n"
+ " ?r ex:prop1 ?v1.\n"
+ " ?r ex:prop2 ?v2.\n"
+ "}\n"
+ "WHERE {\n"
+ " {\n"
+ " SELECT ?r\n"
+ " WHERE {\n"
+ " ?r a dbpedia-owl:Work.\n"
+ " FILTER(EXISTS { ?r dbpedia-owl:originalLanguage [] } && EXISTS { ?r dbpedia-owl:author/dbpedia-owl:birthPlace [] }).\n"
+ " } LIMIT 5\n"
+ " }\n"
+ " ?r dbpedia-owl:originalLanguage ?v1.\n"
+ " ?r dbpedia-owl:author/dbpedia-owl:birthPlace ?v2.\n"
+ "}";
Console.WriteLine(query);
Console.WriteLine();
IGraph graph = endpoint.QueryWithResultGraph(query);
PrintNodes("IGraph.Nodes", graph.Nodes);
Console.WriteLine("All triples from IGraph.Triples:");
foreach (var triple in graph.Triples) {
Console.WriteLine("- S: " + NodeToString(triple.Subject));
Console.WriteLine(" P: " + NodeToString(triple.Predicate));
Console.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);
// Graph Analysis
// The following code tries to retrieve exactly the items of the temporary
// type "record".
var typeNode = TryFindUriNode(graph, new Uri(NamespaceMapper.RDF + "type"));
var recordNode = TryFindUriNode(graph, new Uri("http://www.example.com/record"));
Console.WriteLine();
TryFindAllNodes("subjects", graph, graph.Triples.SubjectNodes.OfType<IUriNode>().Select(node => node.Uri));
TryFindAllNodes("predicates", graph, graph.Triples.PredicateNodes.OfType<IUriNode>().Select(node => node.Uri));
TryFindAllNodes("objects", graph, graph.Triples.ObjectNodes.OfType<IUriNode>().Select(node => node.Uri));
Console.WriteLine();
var createdTypeNode = graph.CreateUriNode(new Uri(NamespaceMapper.RDF + "type"));
var createdRecordNode = graph.CreateUriNode(new Uri("http://www.example.com/record"));
if ((typeNode != null) && (recordNode != null)) {
Console.WriteLine("{0} triple(s) with found predicate and found object.",
graph.GetTriplesWithPredicateObject(typeNode, recordNode).Count());
}
if (typeNode != null) {
Console.WriteLine("{0} triple(s) with found predicate and created object.",
graph.GetTriplesWithPredicateObject(typeNode, createdRecordNode).Count());
}
if (recordNode != null) {
Console.WriteLine("{0} triple(s) with created predicate and found object.",
graph.GetTriplesWithPredicateObject(createdTypeNode, recordNode).Count());
}
Console.WriteLine("{0} triple(s) with created predicate and created object.",
graph.GetTriplesWithPredicateObject(createdTypeNode, createdRecordNode).Count());
}
private static string NodeToString(INode node)
{
return string.Format("{0} ({1})", node, node.GetType().Name);
}
private static void PrintNodes(string title, IEnumerable<INode> nodes)
{
Console.WriteLine(title + ":");
foreach (var node in nodes) {
Console.WriteLine("- " + NodeToString(node));
}
Console.WriteLine();
}
private static INode TryFindUriNode(IGraph graph, Uri uri)
{
var result = graph.GetUriNode(uri);
if (result == null) {
Console.WriteLine(uri.ToString() + " was NOT found by IGraph.GetUriNode.");
} else {
Console.WriteLine(uri.ToString() + " WAS found by IGraph.GetUriNode.");
}
return result;
}
private static void TryFindAllNodes(string title, IGraph graph, IEnumerable<Uri> uris)
{
Console.WriteLine("Trying to find all " + title + ":");
foreach (Uri uri in uris) {
TryFindUriNode(graph, uri);
}
}
}
}
这是示例程序的输出:
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.
可以看出, IGraph.Nodes
枚举不包括谓词Uris,例如 http://www.example.com/prop1
或 http://www.w3.org/1999/02/22-rdf-syntax-ns#type
. 同样,输出显示 GetUriNode
找不到谓词,而主题和对象则是 .
2 回答
您可以使用INodeFactory(
IGraph
extends)中的CreateURINode来创建rdf:type
节点,并具有以下内容:这与我使用
ResourceFactory.createProperty( http://...ns#type )
之类的方法类似 . (实际上,为了方便起见,耶拿有一个常数RDF.type,我用它来提前未定义为常量的那个 . )这种行为完全是设计的,只出现在谓词位置的东西被认为是图形中的边缘而不是图形中的节点 .
由于Working with Graphs文档声明如下:
也许
GetEdge()
和相应的Edges
属性会有用吗?