use XML::LibXML;

my $parser = XML::LibXML->new();
my $doc = $parser->parse_file("type_book.xml");

for my $chapter_node ($doc->findnodes('/book/contents'))
{
	print $chapter_node->findvalue('locator[@href ="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED"]/@title');	
}

##</code><code>##

print $chapter_node->findvalue('locator[@href ="/*releaseStatus=RELEASED"]/@title');	
}

##</code><code>##

<book>
<contents>
<locator href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED" role="http://www.iop.org/roles/book-part-locator" title="Photonic crystal light-emitting sources">
</locator>  
<locator href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=pdf" role="http://www.iop.org/roles/book-part-pdf-locator" title="Photonic crystal light-emitting sources">
</locator>  
<locator href="/book/isbn/979-0-4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;format=epub" role="http://www.iop.org/roles/book-part-epub-locator" title="Photonic crystal light-emitting sources">
</locator>
</contents>
</book>