// Portions Copyright (c) 2006 - 2008, Clark & Parsia, LLC. <http://www.clarkparsia.com>
// Clark & Parsia, LLC parts of this source code are available under the terms of the Affero General Public License v3.
//
// Please see LICENSE.txt for full license terms, including the availability of proprietary exceptions.
// Questions, comments, or requests for clarification: licensing@clarkparsia.com

package org.mindswap.pellet.examples;

import org.mindswap.pellet.PelletOptions;
import org.mindswap.pellet.jena.PelletReasonerFactory;

import com.clarkparsia.pellet.sparqldl.jena.SparqlDLExecutionFactory;
import org.apache.jena.ontology.OntModel;
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.query.ResultSetFormatter;
import org.apache.jena.rdf.model.ModelFactory;
import org.apache.jena.rdf.model.Resource;


/**
 * Bnodes used in a SPARQL query are treated as variables but different from ordinary
 * SPARQL variables they are not required to be bound to existing individuals. This means
 * a bnode in the query can be matched with an individual whose existence is inferred from
 * a someValues or a minCardinality restriction.
 * 
 * @author Evren Sirin
 */
public class BnodeQueryExample {
    public static void main(String[] args) throws Exception { 
    	PelletOptions.TREAT_ALL_VARS_DISTINGUISHED = false;
        String ns = "http://www.w3.org/TR/2003/PR-owl-guide-20031209/food#";
         
        // create an empty ontology model using Pellet spec
        OntModel model = ModelFactory.createOntologyModel( PelletReasonerFactory.THE_SPEC );        
            
        // read the file
        model.read( "file:examples/data/wine.owl" );	  

        // getOntClass is not used because of the same reason mentioned above
        // (i.e. avoid unnecessary classifications)
        Resource RedMeatCourse = model.getResource( ns + "RedMeatCourse" ); 
        Resource PastaWithLightCreamCourse = model.getResource( ns + "PastaWithLightCreamCourse" ); 
        
        // create two individuals Lunch and dinner that are instances of  
        // PastaWithLightCreamCourse and RedMeatCourse, respectively
        model.createIndividual( ns + "MyLunch", PastaWithLightCreamCourse);
        model.createIndividual( ns + "MyDinner", RedMeatCourse);
        
        String queryBegin = 
            "PREFIX rdf:  <http://www.w3.org/1999/02/22-rdf-syntax-ns#>\r\n" + 
            "PREFIX food: <http://www.w3.org/TR/2003/PR-owl-guide-20031209/food#>\r\n" + 
            "PREFIX wine: <http://www.w3.org/TR/2003/PR-owl-guide-20031209/wine#>\r\n" + 
            "\r\n" + 
            "SELECT ?Meal ?WineColor\r\n" + 
            "WHERE {\r\n";
        String queryEnd = "}";
        
        // create a query that asks for the color of the wine that
        // would go with each meal course
        String queryStr1 =
            queryBegin + 
            "   ?Meal rdf:type food:MealCourse .\r\n" + 
            "   ?Meal food:hasDrink _:Wine .\r\n" + 
            "   _:Wine wine:hasColor ?WineColor" +
            queryEnd;

        // same query as above but uses a variable instead of a bnode        
        String queryStr2 =
            queryBegin + 
            "   ?Meal rdf:type food:MealCourse .\r\n" + 
            "   ?Meal food:hasDrink ?Wine .\r\n" + 
            "   ?Wine wine:hasColor ?WineColor" +
            queryEnd;

        Query query1 = QueryFactory.create( queryStr1 );
        Query query2 = QueryFactory.create( queryStr2 );

        // The following definitions from food ontology dictates that 
        // PastaWithLightCreamCourse has white wine and RedMeatCourse 
        // has red wine.
        //  Class(PastaWithLightCreamCourse partial 
		//        restriction(hasDrink allValuesFrom(restriction(hasColor value (White)))))
        //  Class(RedMeatCourse partial 
		//        restriction(hasDrink allValuesFrom(restriction(hasColor value (Red)))))
        //
        // PelletQueryEngine will successfully find the answer for the first query
        printQueryResults( 
            "Running first query with PelletQueryEngine...", 
            SparqlDLExecutionFactory.create( query1, model ), query1 );
        
        // The same query (with variables instead of bnodes) will not return same answers!
        // The reason is this: In the second query we are using a variable that needs to be 
        // bound to a specific wine instance. The reasoner knows that there is a wine (due
        // to the cardinality restriction in the ontology) but does not know the URI for  
        // that individual. Therefore, query fails because no binding can be found. 
        //
        // Note that this behavior is similar to what you get with "must-bind", "don't-bind" 
        // variables in OWL-QL. In this case, variables in the query are "must-bind" variables 
        // and bnodes are "don't-bind" variables.
        printQueryResults( 
            "Running second query with PelletQueryEngine...", 
            SparqlDLExecutionFactory.create( query2, model ), query2 );
        
        // When the standard QueryEngine of Jena is used we don't get the results even 
        // for the first query. The reason is Jena QueryEngine evaluates the query one triple 
        // at a time and thus fails when the wine individual is not found. PelletQueryEngine
        // evaluates the query as a whole and succeeds. (If the above feature, creating bnodes
        // automatically, is added to Pellet then you would get the same results here) 
        printQueryResults( 
            "Running first query with standard Jena QueryEngine...", 
            QueryExecutionFactory.create( query1, model ), query1 );        
    }
    
    public static void printQueryResults( String header, QueryExecution qe, Query query ) throws Exception {
        System.out.println(header);
        
        ResultSet results = qe.execSelect();

		ResultSetFormatter.out( System.out, results, query );
		
		System.out.println();
    }
}
