与Jena的SPARQL解析错误，但DBpedia接受该查询 [英] SPARQL parse error with Jena, but DBpedia accepts the query

问题描述

我正在使用Jena启动SPARQL查询。我有这个代码，产生错误。
我不明白这个错误的原因，因为将查询放入 DBpedia SPARQL端点工作！我认为我正确地编写了查询字符串。什么是错误？

I'm using Jena to launch a SPARQL query. I have this code, which produces an error. I don't understand the reason for this error, since putting the query into the DBpedia SPARQL endpoint works! I think that I wrote the query string correctly. What's the error?

 String sparqlQueryString=
 "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> "+
 "select ?sub ?super (count(?mid) as ?length) where {"+
 "values ?sub { <http://dbpedia.org/ontology/Writer> }" +
 "?sub rdfs:subClassOf* ?mid ."+
 "?mid rdfs:subClassOf+ ?super .}"+
 "group by (?sub ?super)"+
 "order by (?length)";
 query = QueryFactory.create(sparqlQueryString); 
 QueryExecution qexec = 
 QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql",query);

错误

Error

Exception in thread "main" com.hp.hpl.jena.query.QueryParseException: Encountered "     
<VAR1> "?super "" at line 1, column 231.
Was expecting one of:
"not" ...
"as" ...
"in" ...
<INTEGER_POSITIVE> ...
<DECIMAL_POSITIVE> ...
<DOUBLE_POSITIVE> ...
<INTEGER_NEGATIVE> ...
<DECIMAL_NEGATIVE> ...
<DOUBLE_NEGATIVE> ...
")" ...
"=" ...
"!=" ...
">" ...
"<" ...
"<=" ...
">=" ...
"||" ...
"&&" ...
"+" ...
"-" ...
"*" ...
"/" ...
at com.hp.hpl.jena.sparql.lang.ParserSPARQL11.perform(ParserSPARQL11.java:102)
at com.hp.hpl.jena.sparql.lang.ParserSPARQL11.parse$(ParserSPARQL11.java:53)
at com.hp.hpl.jena.sparql.lang.SPARQLParser.parse(SPARQLParser.java:37)
at com.hp.hpl.jena.query.QueryFactory.parse(QueryFactory.java:156)
at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:79)
at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:52)
at com.hp.hpl.jena.query.QueryFactory.create(QueryFactory.java:40)
at Query.QueryRDF.retrieveSuperClasses(QueryRDF.java:87)
at Query.QueryRDF.main(QueryRDF.java:144)

推荐答案

不要'将括号括在 GROUP BY 变量周围。也就是说，它应该是 group by？sub？super ，
而不是 group by（？sub？super）。如果您在查询中添加带有 \ n 的换行符，则非常清楚，这样可以更容易地查看错误的位置。例如，当我尝试编译以下代码时，我得到以下运行时错误。

Dont' put parentheses around the GROUP BY variables. That is, it should be group by ?sub ?super, and not group by (?sub ?super). This is pretty clear if you add newlines with \n to your query, so that it's easier to see where the error is. E.g., when I try to compile the following code, I get the following run time error.

import com.hp.hpl.jena.query.Query;
import com.hp.hpl.jena.query.QueryExecution;
import com.hp.hpl.jena.query.QueryExecutionFactory;
import com.hp.hpl.jena.query.QueryFactory;

public class ParseError {
    @SuppressWarnings("unused")
    public static void main(String[] args) {
         String sparqlQueryString=
                 "PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> \n"+
                 "select ?sub ?super (count(?mid) as ?length) where {\n"+
                 "values ?sub { <http://dbpedia.org/ontology/Writer> }\n" +
                 "?sub rdfs:subClassOf* ?mid .\n"+
                 "?mid rdfs:subClassOf+ ?super .}\n"+
                 "group by (?sub ?super)\n"+
                 "order by (?length)\n";
         Query query = QueryFactory.create(sparqlQueryString); 
         QueryExecution qexec = 
                 QueryExecutionFactory.sparqlService("http://dbpedia.org/sparql",query);
    }
}

线程中的异常 maincom.hp.hpl.jena.query.QueryParseException：Encountered？super在第6行第16列。

Exception in thread "main" com.hp.hpl.jena.query.QueryParseException: Encountered " "?super "" at line 6, column 16.

错误指向有问题的行。这里不需要括号，如 GroupClause 语法中的生产需要一个或多个 GroupCondition s，其格式由此产品定义：

The error points right to the problematic line. Parentheses aren't needed here, as the GroupClause production in the grammar expects one or more GroupConditions, which have a form defined by this production:

GroupCondition :: = BuiltInCall | FunctionCall | '（'表达式（'AS'Var）？'）'| Var

GroupCondition ::= BuiltInCall | FunctionCall | '(' Expression ( 'AS' Var )? ')' | Var

如果有一个 GROUP BY（...）它应该是类似于

If there's a GROUP BY (...) it's supposed to be something like

GROUP BY ( ?a+?b )
GROUP BY ( ?a+?b as ?abSum )

你也可以测试过这个通过粘贴您的查询

You could also have tested this by pasting your query

PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 
select ?sub ?super (count(?mid) as ?length) where {
values ?sub { <http://dbpedia.org/ontology/Writer> }
?sub rdfs:subClassOf* ?mid .
?mid rdfs:subClassOf+ ?super .}
group by (?sub ?super)
order by (?length)

进入 sparql.org的查询验证器您将获得输出：

输入：

Input:

  1 PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> 
  2 select ?sub ?super (count(?mid) as ?length) where {
  3 values ?sub { <http://dbpedia.org/ontology/Writer> }
  4 ?sub rdfs:subClassOf* ?mid .
  5 ?mid rdfs:subClassOf+ ?super .}
  6 group by (?sub ?super)
  7 order by (?length)

语法错误

Syntax Error

Encountered "  "?super "" at line 6, column 16.
Was expecting one of:
    "not" ...
    "as" ...
    "in" ...
     ...

这篇关于与Jena的SPARQL解析错误，但DBpedia接受该查询的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！