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ELK consequence-based reasoning engine

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/*
 * #%L
 * elk-reasoner
 * 
 * $Id$
 * $HeadURL$
 * %%
 * Copyright (C) 2011 Department of Computer Science, University of Oxford
 * %%
 * 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%
 */
package org.semanticweb.elk.reasoner.indexing.hierarchy;

import org.semanticweb.elk.reasoner.indexing.visitors.IndexedClassExpressionVisitor;
import org.semanticweb.elk.reasoner.indexing.visitors.IndexedObjectIntersectionOfVisitor;

/**
 * Represents all occurrences of an ElkObjectIntersectionOf in an ontology.
 * 
 * @author Frantisek Simancik
 * 
 */
public class IndexedObjectIntersectionOf extends IndexedClassExpression {
	/**
	 * There are only two conjuncts. This reflects the fact that conjunctions
	 * are binarized during index construction. The conjuncts may not correspond
	 * to any ElkClassExpression in the ontology.
	 */
	protected final IndexedClassExpression firstConjunct, secondConjunct;

	protected IndexedObjectIntersectionOf(IndexedClassExpression firstConjunct,
			IndexedClassExpression secondConjunct) {
		this.firstConjunct = firstConjunct;
		this.secondConjunct = secondConjunct;
	}

	public IndexedClassExpression getFirstConjunct() {
		return firstConjunct;
	}

	public IndexedClassExpression getSecondConjunct() {
		return secondConjunct;
	}

	public  O accept(IndexedObjectIntersectionOfVisitor visitor) {
		return visitor.visit(this);
	}

	@Override
	public  O accept(IndexedClassExpressionVisitor visitor) {
		return accept((IndexedObjectIntersectionOfVisitor) visitor);
	}

	@Override
	protected void updateOccurrenceNumbers(int increment,
			int positiveIncrement, int negativeIncrement) {

		if (negativeOccurrenceNo == 0 && negativeIncrement > 0) {
			// first negative occurrence of this expression
			firstConjunct.addNegConjunctionByConjunct(this, secondConjunct);
			secondConjunct.addNegConjunctionByConjunct(this, firstConjunct);
		}

		positiveOccurrenceNo += positiveIncrement;
		negativeOccurrenceNo += negativeIncrement;

		if (negativeOccurrenceNo == 0 && negativeIncrement < 0) {
			// no negative occurrences of this conjunction left
			firstConjunct.removeNegConjunctionByConjunct(this, secondConjunct);
			secondConjunct.removeNegConjunctionByConjunct(this, firstConjunct);
		}

	}

	@Override
	public String toString() {
		return "ObjectIntersectionOf(" + this.firstConjunct + ' '
				+ this.secondConjunct + ')';
	}

}