$root_ns = "http://www.xxxx.com/yyy";
$data_ns = "http://www.xxxx.com/zzz";
$prefix_map = {
   $root_ns => 'ROOT-NS',
   $data_ns => ''
};

##</code><code>##

$xml = XML::Writer->new(DATA_MODE => 1, DATA_INDENT => 2, NAMESPACES => 1, PREFIX_MAP => $prefix_map);

##</code><code>##

$xml->startTag([[$data_ns, 'data']]);
$xml->dataElement('test', 'ok');
$xml->endTag();