how to get XML::LibXML perfect xpath query ?

Kanishka.black0 has asked for the wisdom of the Perl Monks concerning the following question:

i have tried to use the LibXML modules to xpath a document but its getting complicated .......... i have seen this example over forum here .........

use XML::LibXML ;
use strict;
use warnings;
{
    my $xml = <<'XML';
<?xml version="1.0" standalone="yes"?>
<sdnList>
  <sdnEntry>
    <lastName>Hello world!</lastName>
  </sdnEntry>
</sdnList>
XML
    my $parser = XML::LibXML->new;
    my $doc    = $parser->parse_string($xml);
    my $result = $doc->findvalue('//lastName');
    print $result;
}
{
    my $xml = <<'XML';
<?xml version="1.0" standalone="yes"?>
<sdnList xmlns="http://tempuri.org/sdnList.xsd">
  <sdnEntry>
    <lastName>Hello world!</lastName>
  </sdnEntry>
</sdnList>
XML
    my $parser = XML::LibXML->new;
    my $doc    = $parser->parse_string($xml);
    my $result = $doc->findvalue('//lastName');
    print $result ;
}
[download]

/ One of the member posted this solution ... /

use XML::LibXML;
use XML::LibXML::XPathContext;

{
    my $xml = <<'XML';
<?xml version="1.0" standalone="yes"?>
<sdnList xmlns="http://tempuri.org/sdnList.xsd">
  <sdnEntry>
    <lastName>Hello world!</lastName>
  </sdnEntry>
</sdnList>
XML
    my $parser = XML::LibXML->new;
    my $doc    = $parser->parse_string($xml);
    my $xc     = XML::LibXML::XPathContext->new($doc);
    $xc->registerNs('sdnList', 'http://tempuri.org/sdnList.xsd');
    my $result = $xc->findvalue('//sdnList:lastName');
    is( $result, "Hello world!", "Namespace" );
}
[download]

But every time we can't get same namespace ... if i add any API to the xml input ..... its extremely difficult to handle it ......

Is there any way to get nodes and attr and like that stuff in XML::LibXML easily ??? or any other modules excpet xml::xpath..

UPDATE ...... i think i have not conveyed the message properly ... about my last part .. .

if the XML page varies every time ... like this ....

lets take one example ... Flickr API http://www.flickr.com/services/api/explore/?method=flickr.photos.getSizes .... here we go .... if give the correct Photo ID i will get this result ...

<rsp stat="ok">
<sizes canblog="1" canprint="0" candownload="0">
<size label="Square" width="75" height="75" source="http://farm5.stati
+c.flickr.com/4007/4673769513_02826f0775_s.jpg" url="http://www.flickr
+.com/photos/dhushor-jen/4673769513/sizes/sq/" media="photo"/>
<size label="Thumbnail" width="100" height="67" source="http://farm5.s
+tatic.flickr.com/4007/4673769513_02826f0775_t.jpg" url="http://www.fl
+ickr.com/photos/dhushor-jen/4673769513/sizes/t/" media="photo"/>
<size label="Small" width="240" height="160" source="http://farm5.stat
+ic.flickr.com/4007/4673769513_02826f0775_m.jpg" url="http://www.flick
+r.com/photos/dhushor-jen/4673769513/sizes/s/" media="photo"/>
<size label="Medium" width="500" height="333" source="http://farm5.sta
+tic.flickr.com/4007/4673769513_02826f0775.jpg" url="http://www.flickr
+.com/photos/dhushor-jen/4673769513/sizes/m/" media="photo"/>
<size label="Large" width="1024" height="683" source="http://farm5.sta
+tic.flickr.com/4007/4673769513_02826f0775_b.jpg" url="http://www.flic
+kr.com/photos/dhushor-jen/4673769513/sizes/l/" media="photo"/>
</sizes>
</rsp>
[download]

what if i give incorrect photo id in the above code ....

<rsp stat="fail">
<err code="1" msg="Photo not found"/>
</rsp>
[download]

Can any one tell me how can write xpath this kind of things ?

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