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AGSparqlFiltersInOptionals.java

package com.franz.agbase.examples;



import com.franz.agbase.*;



public class AGSparqlFiltersInOptionals {



    /**

     * Demonstrates some basics of using FILTER in OPTIONAL graph patterns.

     * 

     * @param args unused

     * @throws AllegroGraphException 

     */

    public static void main(String[] args) throws AllegroGraphException {

        

        // Connect to server, which must already be running.

        AllegroGraphConnection ags = new AllegroGraphConnection();

        try {

            ags.enable();

        } catch (Exception e) {

            throw new AllegroGraphException("Server connection problem", e);

        }

        

        // Create fresh triple-store for this example.

        AllegroGraph ts = ags.renew("sparql", AGPaths.TRIPLE_STORES);

                

        // Register any namespaces

        ts.registerNamespace("dc", "http://purl.org/dc/elements/1.1/");

        ts.registerNamespace("b", "http://example.org/book/");

        ts.registerNamespace("ns", "http://example.org/ns#");



        // Add some data to the store

        ts.addStatement("!b:book1","!dc:title",ts.createLiteral("SPARQL Tutorial"));

        ts.addStatement("!b:book1","!ns:price",ts.createLiteral(42));

        ts.addStatement("!b:book2","!dc:title",ts.createLiteral("The Semantic Web"));

        ts.addStatement("!b:book2","!ns:price",ts.createLiteral(23));



        // Query using a FILTER inside an OPTIONAL graph pattern.  No price 

        // appears for the book with title "SPARQL Tutorial" because the 

        // optional graph pattern did not lead to a solution involving the 

        // variable ?price.

        String query = 

        "PREFIX  dc:  <http://purl.org/dc/elements/1.1/> " +

        "PREFIX  ns:  <http://example.org/ns#> " +

        "SELECT  ?title ?price " +

        "WHERE   { ?x dc:title ?title . " +

                "OPTIONAL { ?x ns:price ?price . FILTER (?price < 30) } " +

                "}";

        

        // Query the store and show the results

        SPARQLQuery sq = new SPARQLQuery();

        sq.setTripleStore(ts);

        sq.setQuery(query);

        AGSparqlSelect.doSparqlSelect(sq);



        // Close the triple store and disconnect from the server.

        ts.closeTripleStore();

        ags.disable();

    }



}
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