/*
 * Copyright (C) 1999-2004 <a href="mailto:mandarax@jbdietrich.com">Jens Dietrich</a>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
package org.mandarax.kernel;

import java.util.Iterator;


/**
 * Set of clauses. Clause sets should be used to pack related clauses (e.g. facts
 * with the same predicate or rules with the same predicates in the head). When the
 * method <code>clauses()</code> is called to retrieve the
 * element of the "set" (better: collection), then the set is actually be built. 
 * Therefore, clause sets can be <em>descriptive</em> containers. A typical application
 * is the on the fly integration of facts from relational databases.  
 * Note that clauses (and thereby facts and rules) itself are treated as clause sets and
 * therefore clause sets are often invisible to the user.
 * Clause sets are the main entities managed by knowledge bases.
 * @see org.mandarax.kernel.KnowledgeBase
 * @see org.mandarax.kernel.Rule
 * @see org.mandarax.kernel.Fact
 * @author <A HREF="mailto:mandarax@jbdietrich.com">Jens Dietrich</A>
 * @version 3.3.1 <9 August 2004>
 * @since 1.0
 */
public interface ClauseSet extends KnowledgeOwner, PropertiesSupport {

    /**
     * Add a clause set listener.
     * @param l the listener
     */
    void addClauseSetChangeListener(ClauseSetChangeListener l);

    /**
     * Get a key for indexing. The knowledge base is supposed to
     * contain only clauses having the same key object. This method
     * returns this key object. Note that this behavior is not enforced!
     * @see org.mandarax.kernel.Fact#getKey
     * @see org.mandarax.kernel.Rule#getKey
     * @return the key object
     */
    public Object getKey() ;

    /**
     * Remove a clause set listener.
     * @param l the listener
     */
    void removeClauseSetChangeListener(ClauseSetChangeListener l);
    /**
     * Get an iterator iterating over the predicates contained in this clause set.
     * @return an iterator
     */
    Iterator predicates();
}
