protected function addObjectIdentityAncestorsTable()
    {
        $table = $this->createTable($this->options['oid_ancestors_table_name']);

        $table->addColumn('object_identity_id', 'integer', array('unsigned' => true));
        $table->addColumn('ancestor_id', 'integer', array('unsigned' => true));

        $table->setPrimaryKey(array('object_identity_id', 'ancestor_id'));

        $oidTable = $this->getTable($this->options['oid_table_name']);
        $table->addForeignKeyConstraint($oidTable, array('object_identity_id'), array('id'), array('onDelete' => 'CASCADE', 'onUpdate' => 'CASCADE'));
        $table->addForeignKeyConstraint($oidTable, array('ancestor_id'), array('id'), array('onDelete' => 'CASCADE', 'onUpdate' => 'CASCADE'));
    }