public function getNode($nodeId)
    {
        static $instance = array();
        if (isset($instance[$nodeId]))
            return $instance[$nodeId];
        $nodes = $this->nodeSet;
        if (empty($nodes))
            return NULL;
        foreach ($nodes as $node):
            if ($node->getId() == $nodeId):
                $instance[$nodeId] = &$node;
                break;
            endif;
        endforeach;
        return NULL;
    }