[jira] [Created] (JENA-445) a problem in rewriting nested query by AlgebraGenerator

["John Liu (JIRA)" <ji...@apache.org>]

John Liu created JENA-445:
-----------------------------

             Summary: a problem in rewriting nested query by AlgebraGenerator
                 Key: JENA-445
                 URL: https://issues.apache.org/jira/browse/JENA-445
             Project: Apache Jena
          Issue Type: Bug
    Affects Versions: Jena 2.10.0
         Environment: Windows
            Reporter: John Liu


I found a problem when rewriting a nested query by AlgebraGenerator, the generated query becomes syntax incorrect query. The version of JENA I tested is 2.7.1 and 2.10.1
 
The code I rewrite the query is:

    Query query = QueryFactory.create(queryString);
     AlgebraGenerator ag =
    new AlgebraGenerator();
    Op op = ag.compile(query);
    Query query2 = OpAsQuery.asQuery(op);

The original query is:

PREFIX dcterms: <http://purl.org/dc/terms/> 
PREFIX dbpedia: <http://dbpedia.org/resource/> 
SELECT ?num_of_holidays ?celebrate_Chinese_New_Year WHERE { 
{SELECT ?country_cat (COUNT(?holiday) as ?num_of_holidays) 
WHERE {?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country>. 
?holiday dcterms:subject ?country_cat 
}GROUP by ?country_cat 
} 
{ 
SELECT ?country_cat (COUNT(?holiday) as ?celebrate_Chinese_New_Year) 
WHERE { 
?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country>. 
?holiday dcterms:subject ?country_cat 
FILTER(?holiday="http://dbpedia.org/resource/Lunar_New_Year's_Day") 
}GROUP by ?country_cat 
} 
}
The generated query is:
SELECT ?country_cat ?celebrate_Chinese_New_Year
WHERE
{ { ?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country> .
?holiday <http://purl.org/dc/terms/subject> ?country_cat
BIND(count(?holiday) AS ?num_of_holidays)
}
{ ?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country> .
?holiday <http://purl.org/dc/terms/subject> ?country_cat
FILTER ( ?holiday = "http://dbpedia.org/resource/Lunar_New_Year's_Day" )
BIND(count(?holiday) AS ?celebrate_Chinese_New_Year)
}
}
GROUP BY ?country_cat

The generated query has a syntax error: "Line 5, column 12: Aggregate expression not legal at this point".

The following  is a java class to demonstrate the problem:

import com.hp.hpl.jena.query.Query;
import com.hp.hpl.jena.query.QueryFactory;
import com.hp.hpl.jena.sparql.algebra.AlgebraGenerator;
import com.hp.hpl.jena.sparql.algebra.Op;
import com.hp.hpl.jena.sparql.algebra.OpAsQuery;

public class TestJena {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		
		String queryString = 
			"PREFIX dcterms: <http://purl.org/dc/terms/> \n" +
			"PREFIX dbpedia: <http://dbpedia.org/resource/> \n" +
				
				"SELECT ?num_of_holidays ?celebrate_Chinese_New_Year  WHERE { \n" +
						"{" +
							"SELECT ?country_cat (COUNT(?holiday) as ?num_of_holidays) \n" +
							"WHERE {" +
								"?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country>. \n" +
								"?holiday dcterms:subject ?country_cat \n" +
							"}GROUP by ?country_cat \n" +
						"} \n" +
					"{ \n" +
					"SELECT ?country_cat (COUNT(?holiday) as ?celebrate_Chinese_New_Year) \n" +
						"WHERE { \n" +
							"?country_cat <http://www.w3.org/2004/02/skos/core#broader> <http://dbpedia.org/resource/Category:Public_holidays_by_country>. \n" +
							"?holiday dcterms:subject ?country_cat \n" +
							"FILTER(?holiday=\"http://dbpedia.org/resource/Lunar_New_Year\'s_Day\") \n" +
						"}GROUP by ?country_cat \n" +
					"} \n" + 
				"}\n";
		
		System.out.println("Original query: \n" + queryString);
		
		Query query = QueryFactory.create(queryString);
		
		AlgebraGenerator ag = new AlgebraGenerator();
		Op op = ag.compile(query);
		
		Query query2 = OpAsQuery.asQuery(op);
		
		String queryString2 = query2.toString();
		
		System.out.println("Update query: \n" + queryString2);
		
		Query newQuery2 = QueryFactory.create(queryString2);
		
		
		
	}

}
 

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