rdfschemamodelenumeration.java

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package edu.stanford.db.rdf.schema;

import org.w3c.rdf.model.*;
import java.util.*;
import org.w3c.rdf.vocabulary.rdf_syntax_19990222.RDF;
import org.w3c.rdf.vocabulary.rdf_schema_19990303.RDFS;

public class RDFSchemaModelEnumeration implements Enumeration {

  /**
   * Enumerates all triples (including derived) for a given model and schema
   */

  Model instances, schema;
  Enumeration statements;
  Enumeration derived;
  Hashtable derivedList;
  Statement current;

  public RDFSchemaModelEnumeration(Model instances, Model schema) throws ModelException {

    this.instances = instances;
    this.schema = schema;
    this.statements = instances.elements();
    derivedList = new Hashtable();
    derived = derivedList.elements();
    current = null;
  }

  public boolean hasMoreElements() {

    if(current != null || derived.hasMoreElements())
      return true;
    try {
      if(statements.hasMoreElements()) {
	fetchNext();
	return true;
      }
    } catch (ModelException any) {}
    return false;
  }

  public Object nextElement() {

    if(current != null) {
      Statement s = current;
      current = null;
      return s;
    } else if(derived.hasMoreElements()) {
      return derived.nextElement();
    } else
      throw new NoSuchElementException("RDFSchemaModelEnumeration");
  }

  private void fetchNext() throws ModelException {

    Statement s = (Statement)statements.nextElement();
    derivedList.clear();
    if(RDF.type.equals(s.predicate())) {
      // find superclasses
      Model superclass = schema.find((Resource)s.object(), RDFS.subClassOf, null);
      //                        Model superclass = schema.find(null, RDFS.subClassOf, null);
      //                        System.out.println("Superclasses of " + s.object() + ": " + superclass.size() + " of " + schema.size());
      if(!superclass.isEmpty()) {
        for(Enumeration en = superclass.elements(); en.hasMoreElements();) {
          Statement d = instances.getNodeFactory().createStatement(s.subject(), RDF.type, ((Statement)en.nextElement()).object() );
          derivedList.put(d, d);
        }
      }
    } else { // check for superproperties
      Model superprop = schema.find(s.predicate(), RDFS.subPropertyOf, null);
      if(!superprop.isEmpty()) {
        for(Enumeration en = superprop.elements(); en.hasMoreElements();) {
          Statement d = instances.getNodeFactory().createStatement(s.subject(), (Resource)((Statement)en.nextElement()).object(), s.object() );
          derivedList.put(d, d);
        }
      }
    }
    derived = derivedList.elements();
    current = s;
  }

}