<?php

$xml = '<?xml version="1.0" encoding="utf-8" ?> 
<documentElement>
    <rows>
        <row>
            <column>1</column>
            <column>David</column>
            <column>Johnson</column>
        </row>
        <row>
            <column>2</column>
            <column>Jack</column>
            <column>Nixon</column>
        </row>
    </rows>
</documentElement>';

$sxml = simplexml_load_string($xml);

$rows = json_decode(json_encode(iterator_to_array($sxml->rows->row, 0)), 1);

var_dump($rows);

array(2) {
  [0]=>
  array(1) {
    ["column"]=>
    array(3) {
      [0]=>
      string(1) "1"
      [1]=>
      string(5) "David"
      [2]=>
      string(7) "Johnson"
    }
  }
  [1]=>
  array(1) {
    ["column"]=>
    array(3) {
      [0]=>
      string(1) "2"
      [1]=>
      string(4) "Jack"
      [2]=>
      string(5) "Nixon"
    }
  }
}