function getNodesInfo($node)
    {
               foreach ($result as  $key => $value)
                        {
                          $items[]=$key;
                        }
                        echo ("-----."n");
                        print_r($items."n");

    getNodesInfo($subNode);
    }

-------
Array
(
    [0] => author
    [1] => title
    [2] => genre
    [3] => price
    [4] => publish_date
    [5] => description
)
-------
Array
(
    [0] => author
    [1] => title
    [2] => genre
    [3] => price
    [4] => publish_date
    [5] => description
)
-------
Array
(
    [0] => book
)

Array
(
    [0] => author
    [1] => title
    [2] => genre
    [3] => price
    [4] => publish_date
    [5] => description
)
-------
Array
(
    [0] => book
)