#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML::Reader;

my $reader = 'XML::LibXML::Reader'->new( location => shift )
    or die "Can't open file.\n";

while ($reader->read) {

    if ('product' eq $reader->name) {
        my $dom = $reader->copyCurrentNode(1);
        print $dom->findvalue('product_id'), "\n";

        for my $attr ($dom->findnodes('attributes/attribute')) {

            my $groups = $attr->findnodes('group');
            for my $group (@$groups) {
                my $gid   = $group->findnodes('id');
                my $gname = $group->findnodes('name');
                print "\tgroup [ $gid : $gname ]\n";
            }

            my $values = $attr->findnodes('value');
            for my $value (@$values) {
                my $vid   = $value->findnodes('id');
                my $vval  = $value->findnodes('value');
                print "\tvalue [ $vid : $vval ]\n";
            }
        }
    }
}