Re: Substitution vs initial bindings: SELECT *

[Holger Knublauch]

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:

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
>