Good morning, all.
This might be a newbie question, so please bear with me...
When using an empty URI, e.g. <> or <#>, as the subject of a statement, I
cannot retrieve that statement from a model using SPARQL.
I'm using Jena 5.6.0. A minimal test case would be:
import static org.junit.jupiter.api.Assertions.assertTrue;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryExecution;
import org.apache.jena.query.QueryExecutionFactory;
import org.apache.jena.query.QueryFactory;
import org.apache.jena.query.ResultSet;
import org.apache.jena.rdf.model.Model;
import org.apache.jena.rdf.model.ModelFactory;
import org.apache.jena.rdf.model.Resource;
import org.apache.jena.rdf.model.ResourceFactory;
import org.apache.jena.rdf.model.StmtIterator;
import org.apache.jena.vocabulary.DCTerms;
import org.junit.jupiter.api.Test;
class PointyBracketsTest {
@Test
void test() {
final Resource r = ResourceFactory.createResource("");
final Model m = ModelFactory.createDefaultModel();
m.add(r, DCTerms.title, "A Title");
// check that the statement is present...
final StmtIterator iter = m.listStatements();
while (iter.hasNext()) {
System.out.println(iter.nextStatement());
}
final String query = "SELECT * WHERE {<> ?p ?o}";
final Query q = QueryFactory.create(query);
try (QueryExecution qexec = QueryExecutionFactory.create(q, m)) {
final ResultSet rs = qexec.execSelect();
assertTrue(rs.hasNext(), "No result found");
}
}
}
When I run the test, it prints out ' [, http://purl.org/dc/terms/title, A
Title] ' and then fails.
I'd expect that the SPARQL query would return the added triple. The test also
fails when I add a triple with non-empty subject (i. e. <#>) and then query
with "SELECT * WHERE {<#> ?p ?o}" so it might be that there is something I've
misunderstood. If I use a full URI, e. g. "urn:example:a-resource", the test
passes.
Any help is very much appreciated. Thanks in advance!
Best,
Lars
