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Posted to users@jena.apache.org by "Lars G. Svensson" <la...@web.de> on 2026/05/04 08:57:41 UTC
Empty URI <> returns empty set when executing SPARQL query
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
Re: Empty URI <> returns empty set when executing SPARQL query
Posted by "Lars G. Svensson" <la...@web.de>.
Am 4. Mai 2026 23:54:15 MESZ schrieb Andy Seaborne <an...@apache.org>:
>
>
>On 04/05/2026 09:57, Lars G. Svensson wrote:
>>
>> class PointyBracketsTest {
>>
>> @Test
>> void test() {
>> final Resource r = ResourceFactory.createResource("");
>
>The API does not resolve URIs - it allows relative URIs. Legacy.
>
>It is not a good idea to use relative URIs in the API.
OK.
>
>> 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}";
>
>That query string is resolved. Parsing (RDF syntax, SPARQL syntax) always resolves URIs.
>
>> final Query q = QueryFactory.create(query);
>
>Parses with default base.
>
>Try:
> // Set the base to something else.
> q.setBaseURI("http://myBase/");
> System.out.println(q);
>
>and you should see the real URI in the query.
Ah, I think I understand. Thank you for the explanation.
Best,
Lars
Re: Empty URI <> returns empty set when executing SPARQL query
Posted by Andy Seaborne <an...@apache.org>.
On 04/05/2026 09:57, Lars G. Svensson wrote:
> 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("");
The API does not resolve URIs - it allows relative URIs. Legacy.
It is not a good idea to use relative URIs in the API.
> 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}";
That query string is resolved. Parsing (RDF syntax, SPARQL syntax)
always resolves URIs.
> final Query q = QueryFactory.create(query);
Parses with default base.
Try:
// Set the base to something else.
q.setBaseURI("http://myBase/");
System.out.println(q);
and you should see the real URI in the 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
Andy