CODEWITHSUNDEEP
rdfjenasemantic-webrdfsbag
user592748
user592748

Reputation: 1234

Get bag (container) that contains a particular RDF resource using Jena

I am have a reference to an object of type com.hp.hpl.jena.rdf.model.Resource that is contained in a Bag. I want to list all the Bags that contain this resource. Is there a function similar to listResourcesWithProperty that can be used to search for the containers. ´

The Bag has no properties added. It only has a collection of resources added using Bag.add(RDFNode o)

Upvotes: 0

Views: 653

Answers (1)

Joshua Taylor
Joshua Taylor

Reputation: 85873

This is actually a bit tricky if you don't have inference available because a number of properties are actually used to indicate RDF container membership. E.g., here's a model with three bags, the first and third of which both contain resouces x and y:

@prefix :      <http://stackoverflow.com/q/23568540/1281433/> .
@prefix rdf:   <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .

:Bag1   a       rdf:Bag ;
        rdf:_1  :x ;
        rdf:_2  :y .

:Bag2   a       rdf:Bag ;
        rdf:_1  :y .

:Bag3   a       rdf:Bag ;
        rdf:_1  :y ;
        rdf:_2  :x .

The problem, of course, is that the properties that the first and third bag to, e.g., the resource x are not the same. However, each of those rdf:_nnn properties is an instance of rdfs:ContainerMembershipProperty. In turn, each rdfs:ContainerMembershipProperty is a superproperty of rdfs:member. This means that if you have a reasoner that can infer that, you can ask what resources have x (or y) as an rdfs:member. It doesn't seem (as shown by the following example) that Jena's RDFS reasoners do this. As such, you might just have to iterate over statements that have x as an object, and check whether the property is a container membership property.

import org.apache.jena.riot.Lang;
import org.apache.jena.riot.RDFDataMgr;

import com.hp.hpl.jena.ontology.OntModel;
import com.hp.hpl.jena.ontology.OntModelSpec;
import com.hp.hpl.jena.rdf.model.Bag;
import com.hp.hpl.jena.rdf.model.Model;
import com.hp.hpl.jena.rdf.model.ModelFactory;
import com.hp.hpl.jena.rdf.model.ResIterator;
import com.hp.hpl.jena.rdf.model.Resource;
import com.hp.hpl.jena.rdf.model.Statement;
import com.hp.hpl.jena.rdf.model.StmtIterator;
import com.hp.hpl.jena.vocabulary.RDF;
import com.hp.hpl.jena.vocabulary.RDFS;


public class BagExample {
    public static void main(String[] args) {
        Model model = ModelFactory.createDefaultModel();
        String NS = "http://stackoverflow.com/q/23568540/1281433/";
        model.setNsPrefix( "", NS );
        model.setNsPrefix( "rdf", RDF.getURI() );

        Bag bag1 = model.createBag( NS+"Bag1" );
        Bag bag2 = model.createBag( NS+"Bag2" );
        Bag bag3 = model.createBag( NS+"Bag3" );

        Resource x = model.createResource( NS+"x" );
        Resource y = model.createResource( NS+"y" );

        bag1.add( x ).add( y );
        bag2.add( y );
        bag3.add( y ).add( x );

        RDFDataMgr.write( System.out, model, Lang.TURTLE );

        System.out.println( "=== Bags with X (no inference) ===" );
        ResIterator bagsWithX = model.listSubjectsWithProperty( RDFS.member, x );
        while ( bagsWithX.hasNext() ) {
            System.out.println( bagsWithX.next() );
        }

        System.out.println( "=== Bags with X (RDFS inference) ===" );
        OntModel rdfsModel = ModelFactory.createOntologyModel( OntModelSpec.RDFS_MEM_TRANS_INF, model );
        bagsWithX = rdfsModel.listSubjectsWithProperty( RDFS.member, x );
        while ( bagsWithX.hasNext() ) {
            System.out.println( bagsWithX.next() );
        }


        System.out.println( "=== Bags with X (manual checking) ===" );
        StmtIterator xStmts = model.listStatements( null, null, x );
        while ( xStmts.hasNext() ) {
            Statement s = xStmts.next();
            // This checks whether the URI begins with rdf:_.  A proper
            // solution would make sure that the suffix is actually numeric.
                    // You might also want to check whether the subject actually is 
                    // a Bag.  It could be a member of other kinds of containers, too.
            if ( s.getPredicate().getURI().startsWith( RDF.getURI()+"_" ) ) {
                System.out.println( s.getObject() );
            }
        }
    }
}

=== Bags with X (no inference) ===
=== Bags with X (RDFS inference) ===
=== Bags with X (manual checking) ===
http://stackoverflow.com/q/23568540/1281433/x
http://stackoverflow.com/q/23568540/1281433/x

Upvotes: 1

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