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

use XML::LibXML;

my $xml  = XML::LibXML->load_xml(IO => *DATA);
my $root = $xml->documentElement;
my $chapter_node = $root->findnodes('book:chapter')->[0];
print $chapter_node->findvalue('./book:locator/@*') . "\n";

__DATA__
<book xmlns:book='b'> <!-- Namespace definition missing in the original data -->
<book:chapter id="bk444444ch1" type="CHAPTER">
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED" xlink:title="Photonic crystal light-emitting sources" xlink:type="locator" xmlns:xlink="http://www.w3.org/1999/xlink"/>
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=pdf" xlink:title="Photonic crystal light-emitting sources" xlink:type="locator" xmlns:xlink="http://www.w3.org/1999/xlink"/>
<book:locator xlink:href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=epub" xlink:title="Photonic crystal light-emitting sources" xlink:type="locator" xmlns:xlink="http://www.w3.org/1999/xlink"/>
</book:chapter> <!-- Missing in the original data -->
</book>