$start = {
          'lineitem' => {
                          'invoice' => 1
                        },
          'invoice' => {
                         'lineitem' => 1,
                         'claim' => 1
                       },
          'insurer' => {
                         'claim' => 1
                       },
          'claim' => {
                       'invoice' => 1,
                       'insurer' => 1
                     }
        };

$end = [
    [
        'invoice',
        'claim',
        'insurer',
        'lineitem',
     ],
];