api/src/main/java/org/apache/clerezza/ImmutableGraph.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor  license  agreements.  See the NOTICE file distributed
 * with this work  for  additional  information  regarding  copyright
 * ownership.  The ASF  licenses  this file to you 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.
 */
package org.apache.clerezza;

/**
 * A graph, modeled as a set of triples.
 * This interface does not extend java.util.Set because of the different
 * identity constraints, i.e. two <code>Graph</code>s may be equal (isomorphic)
 * even if the set of triples are not.
 * <p>
 * Implementations MUST be immutable and throw respective exceptions, when
 * add/remove-methods are called.
 *
 * @author reto
 * @see org.apache.clerezza.rdf.core.impl.AbstractGraph
 */
public interface ImmutableGraph extends Graph {

    /**
     * Returns true if two graphs are isomorphic
     *
     * @return true if two graphs are isomorphic
     */
    @Override
    public boolean equals(Object obj);

    /**
     * Return the sum of the blank-nodes independent hashes of the triples.
     * More precisely the hash of the triple is calculated as follows:
     * (hash(subject) >> 1) ^  hash(hashCode) ^ (hash(hashCode) << 1)
     * Where the hash-fucntion return the hashCode of the argument
     * for grounded arguments and 0 otherwise.
     *
     * @return hash code
     */
    @Override
    public int hashCode();
}