[英]Can't get results due to typed literal (xsd:string) querying SPARQL from Jena;
我的Virtuoso服务器运行了已加载的本体,下面的查询通过将其粘贴到Web上sparql端点的文本字段中来工作( ronto,由于安全原因而跳过了本体的前缀(对不起),但我确定它是正确定义,因为查询有效,但返回空列表,这是一个问题 ):
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
select distinct (str(?p) as ?theme) where {?s ronto:isin "id-XXXX"^^xsd:string; ronto:mainThemes ?p}
以下内容不起作用 (返回空列表); 介意跳过
xsd:string
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
select distinct (str(?p) as ?theme) where {?s ronto:isin "id-XXXX"; ronto:mainThemes ?p}
所以, 问题 :我无法从Java获得相同的结果,Jena deps是:
<dependency>
<groupId>org.apache.jena</groupId>
<artifactId>jena-arq</artifactId>
<version>3.0.1</version>
</dependency>
<dependency>
<groupId>org.apache.jena</groupId>
<artifactId>jena-core</artifactId>
<version>3.0.1</version>
</dependency>
因此,玩具代码:
public static void main(String[] args) {
String isin = "id-XXXX";
final ParameterizedSparqlString qs = new ParameterizedSparqlString(
"select ?p where {?s ronto:isin ?isin^^xsd:string; ronto:mainThemes ?p.}");
qs.setBaseUri(base);
qs.setNsPrefix("owl", "http://www.w3.org/2002/07/owl#");
qs.setNsPrefix("xsd", "http://www.w3.org/2001/XMLSchema#");
qs.setNsPrefix("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#");
qs.setNsPrefix("rdfs", "http://www.w3.org/2000/01/rdf-schema#");
qs.setLiteral("isin", isin);
System.out.println("Running as a query " +qs.asQuery());
try (QueryExecution exec = QueryExecutionFactory.sparqlService(publicSparqlEndpoint, qs.asQuery())) {
final ResultSet resultSet = exec.execSelect();
System.out.println(exec.getQuery());
ResultSetFormatter.out(resultSet);
}
System.out.println("Running as a string " + qs.toString());
try (QueryExecution exec = QueryExecutionFactory.sparqlService(publicSparqlEndpoint, qs.toString())) {
final ResultSet resultSet = exec.execSelect();
System.out.println(exec.getQuery());
ResultSetFormatter.out(resultSet);
}
和输出是
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?p
WHERE
{ ?s ronto:isin "id-XXXX" ;
ronto:mainThemes ?p
}
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?p
WHERE
{ ?s ronto:isin "id-XXXX" ;
ronto:mainThemes ?p
}
-----
| p |
=====
-----
Running as a string
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
select ?p where {?s ronto:isin "id-XXXX"^^xsd:string; ronto:mainThemes ?p.}
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX owl: <http://www.w3.org/2002/07/owl#>
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?p
WHERE
{ ?s ronto:isin "id-XXXX" ;
ronto:mainThemes ?p
}
-----
| p |
=====
-----
其中p-box是端点的空列表结果;
我测试了一些不基于类型文字的简单查询(此处为xsd:string),它们给了我非空的结果。
因此,很容易发现exec对象具有跳过了xsd:string的查询,我猜这是一个导致获取空列表的问题,但是为什么它以这种方式工作,什么是解决此问题的干净方法?
解决方案我感谢@AndyS(注意两个更改:查询中的FILTER和QueryEngineHTTP):
public static void main(String[] args) {
String isin = "id-XXXX";
final ParameterizedSparqlString qs = new ParameterizedSparqlString(
"select ?p where {?s ronto:isin ?X; ronto:mainThemes ?p. FILTER (?X= ?isin^^xsd:string)}");
qs.setBaseUri(base);
qs.setNsPrefix("owl", "http://www.w3.org/2002/07/owl#");
qs.setNsPrefix("xsd", "http://www.w3.org/2001/XMLSchema#");
qs.setNsPrefix("rdf", "http://www.w3.org/1999/02/22-rdf-syntax-ns#");
qs.setNsPrefix("rdfs", "http://www.w3.org/2000/01/rdf-schema#");
qs.setNsPrefix("ronto", "....");
qs.setLiteral("isin", isin);
System.out.println("Running as a string " + qs.toString());
try (QueryEngineHTTP exec = new QueryEngineHTTP(publicSparqlEndpoint, qs.toString())) {
final ResultSet resultSet = exec.execSelect();
System.out.println(exec.getQuery());
ResultSetFormatter.out(resultSet);
}
}
在RDF 1.1中,不带xsd:string
和带xsd:string
是相同的RDF术语。 是否编写^^xsd:string
没有关系。
ARQ打印不带^^xsd:string
查询,这用于远程SPARQL调用。
看来Virtuoso实例与RDF 1.1不兼容。
您可以在查询中尝试值表达式:
{ ?s ronto:isin ?X;
ronto:mainThemes ?p.
FILTER ( ?X = "id-XXXX"^^xsd:string)
}
适用于RDF 1.0和RDF 1.1以及系统混合。
或者,直接使用QueryEngineHTTP
,而不是QueryExecutionFactory
。 这允许应用程序将字符串作为查询传递给远程端点,而无需解析或检查。
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