https://github.com/apache/jena/issues/2799
On 21/10/2024 17:45, Andy Seaborne wrote:
On 21/10/2024 08:26, Holger Knublauch wrote:
On 20 Oct 2024, at 9:56 PM, Andy Seaborne <a...@apache.org> wrote:
On 19/10/2024 12:43, Holger Knublauch wrote:
Hi Andy,
I don't know what the expected behaviour should be so it's hard to
define a test with an assertion.
But here is an executable example:
Excellent.
The simple query shows it isn't FILTER or EXISTS related.
Do you agree that it would be better if substitution would expand
SELECT * to how initialBinding behaves?
I neither agree nor disagree at the moment. It looks OK, but there
are other use cases to consider. InitialBindings was limiting from
both a query optimizer point-of-view and parametrized queries for
remote execution.
A workaround for the current release seems to be:
Query query = QueryFactory.create(....)
query.setQueryResultStar(false);
Thanks for this workaround.
FWIW we noticed a related slight difference when a variable on the
right of a BIND was pre-bound. This used to work with initialBindings,
although I think it was illegal already and perhaps a leftover from
the LET days. So I believe we need to eliminate those legacy solutions
anyway.
Correct - they should not work.
Can you already anticipate at which Jena version you will delete
initialBindings? Asking because it may be best for us to stick to
initialBindings and activate substitution as a flag only for a couple
of releases until we have fully identified all cases that need to be
adjusted.
There are several factors:
1. Java25 is LTS and due September 2025. Jena has typically moved
forward with a major release to keep the supported JDKs at "last two
LTS" when it's clear that the LTS has no major problems. A major Jena
release is a time to clearup things.
2. Depending on how RDF 1.2 goes - the WG includes errata, so I hope
EXISTS gets clarified as proposed in SEP-0007. It would be good to align
the syntax-based approach and the algebra changes. The current
rechartering extends the WG of a year then a year in maintenance and new
features mode". That would put a one year on aligning approaches.
3. Initial bindings may become a restriction to work on query
optimization. Deprecated means "at risk".
Andy
Thanks
Holger
I haven't looked at nested SELECTs yet.
(Needless to say this impacts SHACL-SPARQL).
That's a whole subject in itself.
This syntax-based substitution is very similar to SEP-0007 [1] but
that is injection into the algebra. It keeps the variables names in
place (e.g. BOUND).
Andy
[1]
https://github.com/w3c/sparql-dev/blob/main/SEP/SEP-0007/sep-0007.md
import java.util.List;
import org.apache.jena.query.Query;
import org.apache.jena.query.QueryExecutionDatasetBuilder;
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.sparql.core.Var;
import org.apache.jena.sparql.engine.binding.Binding;
import org.apache.jena.vocabulary.OWL;
import org.apache.jena.vocabulary.RDF;
import org.apache.jena.vocabulary.RDFS;
public class SelectStarSubstitutionTest {
public static void main(String[] args) {
Model model = ModelFactory.createDefaultModel();
model.add(OWL.Thing, RDF.type, OWL.Class);
model.add(OWL.Nothing, RDF.type, RDFS.Class);
Query query = QueryFactory.create("SELECT * { ?this a ?
type }");
ResultSet rs = QueryExecutionDatasetBuilder.create().
query(query).
model(model).
//
initialBinding(Binding.builder().add(Var.alloc("this"),
OWL.Thing.asNode()).build()).
substitution("this", OWL.Thing).
select();
List<String> vars = rs.getResultVars();
System.out.println(vars.size());
}
}
The output as shown is 1. If we use initialBinding instead of
substitution, the output is 2.
Do you agree that it would be better if substitution would expand
SELECT * to how initialBinding behaves?
One reason is that this would return 0 results if ?type is replaced
with a constant.
Another reason is that it makes the behaviour inconsistent when it
returns different variables depending on whether
a variable is pre-bound or not, e.g. when people use such SPARQL
queries with optional parameters.
(Needless to say this impacts SHACL-SPARQL).
Thanks
Holger
On 17 Oct 2024, at 1:42 PM, Andy Seaborne <a...@apache.org> wrote:
On 17/10/2024 11:35, Holger Knublauch wrote:
Hi all,
we are trying to switch to Jena 5 and from using
setInitialBindings to substitution.
There is a change in behaviour of SELECT *
Consider a query such as
SELECT *
WHERE
{ ?this ?PATH ?value
FILTER EXISTS { ?value (rdfs:subClassOf)* ?class
FILTER ( ?class IN (rdfs:Class, rdf:Property,
sh:Shape) )
}
}
where ?this and ?PATH have initial bindings.
Using initialBindings, the result variables include ?this, but
with substitution semantics, only ?value is returned.
Does this mean that queries need to be rewritten to explicitly
state SELECT ?this ?value ... ?
Thanks,
Holger
Hi Holger,
Minimal, complete test case please.
(Presumably ?PATH is a property not a more general path)
Andy
