[JENA-2335] Query -> Algebra -> Query not equivalent in case of a BIND not in the result vars

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Delivered
• Affects Version/s: Jena 4.5.0
• Fix Version/s: Jena 4.6.0
• Component/s: ARQ, Optimizer
• Assignee: Andy Seaborne
• Reporter: Jan Martin Keil
• Created: 29/Jun/22 15:25
• Updated: 25/Aug/22 09:43
• Resolved: 05/Jul/22 12:27

Description

Converting a query into algebra and back results in a not equivalent query, if the query contains a BIND clause thous variable is not part of the result variables, but other variables depend on it. Minimal example:

import static org.junit.jupiter.api.Assertions.assertTrue;

import org.apache.jena.query.QueryFactory;
import org.apache.jena.sparql.algebra.AlgebraGenerator;
import org.apache.jena.sparql.algebra.OpAsQuery;
import org.junit.jupiter.api.Test;

public class OpTest {
	@Test
	public void retainVariables() {
		String sparqlStrBeforOp = "SELECT ?a ?d WHERE { ?a <http://example.org/p> ?b . BIND(?b AS ?c) BIND(?c AS ?d) }";
		String sparqlStrAfterOp = OpAsQuery.asQuery(new AlgebraGenerator().compile(QueryFactory.create(sparqlStrBeforOp))).toString();
		System.out.println(sparqlStrAfterOp);
		assertTrue(sparqlStrAfterOp.contains("(?b AS ?c)"));
	}
}

This results in the following query:

SELECT  ?a (?c AS ?d)
WHERE
  { ?a  <http://example.org/p>  ?b }

Use case: I do the conversion back and forth to remove not needed result variables of a given query on algebra level, which is not possible on queries directly.

Issue Links

• links to: GitHub Pull Request #1423