code: package it.unibz.inf.ontop.spec.ontology.impl;
  
  /*
   * #%L
   * ontop-obdalib-core
   * %%
   * Copyright (C) 2009 - 2014 Free University of Bozen-Bolzano
   * %%
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   * 
   *      http://www.apache.org/licenses/LICENSE-2.0
   * 
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   * #L%
   */
  
  import it.unibz.inf.ontop.model.vocabulary.OWL;
  import it.unibz.inf.ontop.spec.ontology.ObjectPropertyExpression;
  import it.unibz.inf.ontop.spec.ontology.ObjectSomeValuesFrom;
  import org.apache.commons.rdf.api.IRI;
  
  /**
   * Represents ObjectPropertyExpression from the OWL 2 QL Specification
   * 
   * ObjectPropertyExpression := ObjectProperty | InverseObjectProperty
   * InverseObjectProperty := 'ObjectInverseOf' '(' ObjectProperty ')'
   * 
   * Support for owl:topObjectProperty and owl:bottomObjectProperty
   *     - the inverses of the two coincide with themselves (rule [R6])
   * 
   * @author Roman Kontchakov
   *
   */
  
  
  public class ObjectPropertyExpressionImpl implements ObjectPropertyExpression {
  
  	private final boolean isInverse;
  	private final IRI iri;
  	private final String string;
  	private final ObjectPropertyExpressionImpl inverseProperty;
  	
  	private final ObjectSomeValuesFromImpl domain;
  	
  	private final boolean isTop, isBottom;
  	
  	static final ObjectPropertyExpression owlTopObjectProperty = new ObjectPropertyExpressionImpl(OWL.TOP_OBJECT_PROPERTY);
  	static final ObjectPropertyExpression owlBottomObjectProperty = new ObjectPropertyExpressionImpl(OWL.BOTTOM_OBJECT_PROPERTY);
  
  	ObjectPropertyExpressionImpl(IRI iri) {
  		this.iri = iri;
  		this.isInverse = false;
  		this.string = iri.getIRIString();
  		this.isTop = iri.equals(OWL.TOP_OBJECT_PROPERTY);
  		this.isBottom = iri.equals(OWL.BOTTOM_OBJECT_PROPERTY);
  		if (isTop || isBottom) 
  			this.inverseProperty = this;   // rule [R6] 
  		else
  			this.inverseProperty = new ObjectPropertyExpressionImpl(iri, this);
  		
  		this.domain = new ObjectSomeValuesFromImpl(this);
  	}
  
  
  
  	/**
  	 * special constructor for creating the inverse of an object property
  	 *  (this constructor is never applied to the top and bottom properties)
  	 *
  	 * @param iri
  	 * @param inverseProperty
  	 */
  
  	private ObjectPropertyExpressionImpl(IRI iri, ObjectPropertyExpressionImpl inverseProperty) {
  		this.iri = iri;
  		this.isInverse = true; // always inverted
  		this.isTop = false; // cannot be the top property
  		this.isBottom = false; // cannot be the bottom property
  		this.inverseProperty = inverseProperty;
  		this.string = iri.getIRIString() + "^-"; // always inverted
  		this.domain = new ObjectSomeValuesFromImpl(this);
  	}
  
  	@Override
  	public boolean isInverse() {
  		return isInverse;
  	}
  
  	@Override
  	public IRI getIRI() {
  		return iri;
  	}
  
  	@Override
  	public ObjectPropertyExpression getInverse() {
  		return inverseProperty;
  	}	
  
  
  	@Override
  	public ObjectSomeValuesFrom getDomain() {
  		return domain;
  	}
  
  	@Override
  	public ObjectSomeValuesFrom getRange() {
  		return inverseProperty.domain;
  	}
  	
  	
  	@Override
  	public boolean equals(Object obj) {
  		if (obj == this)
  			return true;
  
  		if (obj instanceof ObjectPropertyExpressionImpl) {
  			ObjectPropertyExpressionImpl other = (ObjectPropertyExpressionImpl) obj;
  			return (isInverse == other.isInverse) && iri.equals(other.iri);
  		}
  		
  		// the two types of properties share the same name space
  		if (obj instanceof DataPropertyExpressionImpl) {
  			DataPropertyExpressionImpl other = (DataPropertyExpressionImpl) obj;
  			return !isInverse && iri.equals(other.getIRI());
  		}
  		return false;
  	}
  
  	@Override
  	public int hashCode() {
  		return string.hashCode();
  	}
  	
  	@Override
  	public String toString() {
  		return string;
  	}
  
  	@Override
  	public boolean isBottom() {
  		return isBottom;
  	}
  
  	@Override
  	public boolean isTop() {
  		return isTop;
  	}
  }
  