D2RQ映射MySQL数据库后SPARQL查询无结果求助

问题背景 #

配置D2RQ将MySQL数据库转为RDF并通过SPARQL查询，数据库连接正常，SQL查询可获取关联数据，但SPARQL查询?knowledge ont:relatesTo ?genre无结果，仅基础三元组查询能返回genre表部分数据。

配置详情 #

本体文件（my_ontology.owl） #

<?xml version="1.0"?>
<rdf:RDF xmlns="http://example.org/ontology#"
     xml:base="http://example.org/ontology"
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:owl="http://www.w3.org/2002/07/owl#"
     xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
     xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#">
    <owl:Ontology rdf:about="http://example.org/ontology"/>
    
    <!-- Class Genre -->
    <owl:Class rdf:about="http://example.org/ontology#Genre"/>
    
    <!-- Subclasses of Genre -->
    <owl:Class rdf:about="http://example.org/ontology#Person">
        <rdfs:subClassOf rdf:resource="http://example.org/ontology#Genre"/>
    </owl:Class>
    <owl:Class rdf:about="http://example.org/ontology#Organization">
        <rdfs:subClassOf rdf:resource="http://example.org/ontology#Genre"/>
    </owl:Class>

    <!-- Class Knowledge -->
    <owl:Class rdf:about="http://example.org/ontology#Knowledge"/>
    
    <!-- Property relatesTo -->
    <owl:ObjectProperty rdf:about="http://example.org/ontology#relatesTo">
        <rdfs:domain rdf:resource="http://example.org/ontology#Knowledge"/>
        <rdfs:range rdf:resource="http://example.org/ontology#Genre"/>
    </owl:ObjectProperty>
</rdf:RDF>

原映射文件（mapping.ttl） #

@prefix map: <#> .
@prefix db: <> .
@prefix vocab: <vocab/> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix d2rq: <http://www.wiwiss.fu-berlin.de/suhl/bizer/D2RQ/0.1#> .
@prefix jdbc: <http://d2rq.org/terms/jdbc/> .

# Load ontology
map:ontology a d2rq:File;
    d2rq:dataStorage map:database;
    d2rq:fileName "C:/Users/samue/OneDrive/Desktop/my_ontology.owx".

map:database a d2rq:Database;
    d2rq:jdbcDriver "com.mysql.cj.jdbc.Driver";
    d2rq:jdbcDSN "jdbc:mysql://localhost:3306/my_database";
    d2rq:username "root";
    d2rq:password "test123";
    jdbc:zeroDateTimeBehavior "convertToNull";
    jdbc:autoReconnect "true";
    .

# Table genre mapping
map:Genre a d2rq:ClassMap;
    d2rq:dataStorage map:database;
    d2rq:class <http://example.org/ontology#Genre>;
    d2rq:uriPattern "genre/@@genre.genre_id@@";
    d2rq:classDefinitionLabel "genre";
    d2rq:labelColumn "genre.genre_name".

# Table knowledge mapping
map:Knowledge a d2rq:ClassMap;
    d2rq:dataStorage map:database;
    d2rq:class <http://example.org/ontology#Knowledge>;
    d2rq:uriPattern "knowledge/@@knowledge.knowledge_id@@";
    d2rq:classDefinitionLabel "knowledge";
    d2rq:labelColumn "knowledge.label".

# Table knowledge_to_genre mapping
map:KnowledgeToGenre a d2rq:ClassMap;
    d2rq:dataStorage map:database;
    d2rq:class <http://example.org/ontology#KnowledgeToGenre>;
    d2rq:uriPattern "knowledge_to_genre/@@knowledge_to_genre.knowledge_id@@_@@knowledge_to_genre.genre_id@@".

# Mapping for relatesTo property
map:Knowledge_Genre_Relation a d2rq:PropertyBridge;
    d2rq:belongsToClassMap map:Knowledge;
    d2rq:property <http://example.org/ontology#relatesTo>;
    d2rq:refersToClassMap map:Genre;
    d2rq:join "knowledge.knowledge_id = knowledge_to_genre.knowledge_id";
    d2rq:join "genre.genre_id = knowledge_to_genre.genre_id".

正常SQL查询 #

SELECT * FROM knowledge
JOIN knowledge_to_genre ON knowledge.knowledge_id = knowledge_to_genre.knowledge_id
JOIN genre ON genre.genre_id = knowledge_to_genre.genre_id;

无结果SPARQL查询 #

PREFIX ont: <http://example.org/ontology#>
SELECT ?knowledge ?genre
WHERE {
  ?knowledge ont:relatesTo ?genre .
}
LIMIT 10

问题排查与解决方案 #

1. 本体文件路径拼写错误 #

原映射中本体文件名为my_ontology.owx，实际文件是my_ontology.owl，修正路径：

map:ontology a d2rq:File;
    d2rq:dataStorage map:database;
    d2rq:fileName "C:/Users/samue/OneDrive/Desktop/my_ontology.owl".

2. PropertyBridge关联配置错误 #

原PropertyBridge未正确引入中间关联表knowledge_to_genre，D2RQ需要明确指定多表关联的中间表。有两种修正方式：

方式一：使用d2rq:additionalTable直接引入中间表

移除不必要的map:KnowledgeToGenre ClassMap（本体中无对应类），修改PropertyBridge：

# 移除原map:KnowledgeToGenre配置

# Mapping for relatesTo property
map:Knowledge_Genre_Relation a d2rq:PropertyBridge;
    d2rq:belongsToClassMap map:Knowledge;
    d2rq:property <http://example.org/ontology#relatesTo>;
    d2rq:refersToClassMap map:Genre;
    d2rq:join "knowledge.knowledge_id = knowledge_to_genre.knowledge_id";
    d2rq:join "knowledge_to_genre.genre_id = genre.genre_id";
    d2rq:additionalTable "knowledge_to_genre".

方式二：使用d2rq:viaClassMap关联中间表ClassMap

先在本体中添加KnowledgeToGenre类，或保留原ClassMap，修改PropertyBridge：

# Mapping for relatesTo property
map:Knowledge_Genre_Relation a d2rq:PropertyBridge;
    d2rq:belongsToClassMap map:Knowledge;
    d2rq:property <http://example.org/ontology#relatesTo>;
    d2rq:viaClassMap map:KnowledgeToGenre;
    d2rq:refersToClassMap map:Genre;
    d2rq:join "knowledge.knowledge_id = knowledge_to_genre.knowledge_id";
    d2rq:join "knowledge_to_genre.genre_id = genre.genre_id".

3. 验证映射正确性 #

使用D2RQ的dump-rdf工具生成部分RDF数据，检查是否存在relatesTo属性的三元组：

dump-rdf -o output.rdf mapping.ttl

打开output.rdf搜索relatesTo，确认关联三元组已生成。

4. 检查表名/字段名大小写一致性 #

MySQL在Linux系统下表名/字段名区分大小写，确保映射中的表名（如knowledge、genre）与数据库实际表名完全一致。

内容的提问来源于stack exchange，提问作者Samuel Rehkämper