Check out the expat parser. All the info you need is in the PHP docs.
If you just want to put them into a database you can just go through without storing any tree information and pull out "feature_id" and "feature_name" every time you hit a "feature" element.
In start_element() you'll want something like
function start_element($parser, $name, $attrs) {
if($name == "feature") {
if ( isset($attrs("feature_id"))
&& isset($attrs("feature_name")) ) {
$eleFeatures[$attrs("feature_id")] = $attrs("feature_name");
}
}
Or something like that.