The xml is as below:

<book:bookResource xmlns:book="http://api.iop.org/Book/1.0/">
<book:book>
<book:meta doi="10.1088/bk111111" publisherId="bk111111" publisher="Pu
+blishing" platform="science">
</book:meta>
<book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/
+book/isbn/979-0-
4444-1000-17?releaseStatus=RELEASED" xlink:title="979-0-4444-1000-17"
xlink:type="locator">
</book:locator>
<book:contents>
<book:chapter id="bk444444ch1" type="CHAPTER">
<book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/
+book/isbn/979-0-
4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED"
xlink:role="http://www.iop.org/roles/book-part-locator" xlink:title="P
+hotonic crystal
light-emitting sources" xlink:type="locator"></book:locator>  
<book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/
+book/isbn/979-0-
4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;
+format=pdf"
xlink:role="http://www.iop.org/roles/book-part-pdf-locator" xlink:titl
+e="Photonic
crystal light-emitting sources" xlink:type="locator"></book:locator>  
<book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="/
+book/isbn/979-0-
4444-1000-17/book-part/chapter/bk444444ch1?releaseStatus=RELEASED&amp;
+format=epub"
xlink:role="http://www.iop.org/roles/book-part-epub-locator" xlink:tit
+le="Photonic
crystal light-emitting sources" xlink:type="locator"></book:locator>  
<book:meta doi="10.1088/bk444444ch1" firstPage="1-1" lastPage="1-118">
+ 
<book:author givenName="J E" surname="Field"> 
<book:affiliation xmlns:xlink="http://www.w3.org/1999/xlink"
xlink:href="bk444444ch1af1"
xlink:role="http://www.iop.org/roles/affiliation-locator" xlink:type="
+locator">
</book:affiliation>
</book:author>  
<book:affiliation name="Cavendish Laboratory, University of Cambridge"
+> 
<book:locator xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="b
+k444444ch1af1"
xlink:role="http://www.iop.org/roles/affiliation-locator" xlink:type="
+locator">
</book:locator> 
</book:affiliation> 
</book:meta> 
</book:chapter>  
</book:contents>
</book:book>
</book:bookResource>
[download]

The complete code is :

my %book_columns = (
                     'Book_Id' => '@publisherId',
                     'Book_Platform' => '@platform',
                     'Book_Publisher' => '@publisher',
                    );

my %chapter_columns = (
                        'Chapter_Doi' => 'book:meta/@doi',
                        'Chapter_Doi_Prefix' => 'substring-before(book
+:meta/@doi,"/")',
                        'Chapter_Id' => '@id',
                        'Chapter_Title' => 'book:locator[contains(@xli
+nk:href, "format=epub")]/@xlink:title',                        
                      );
[download]

my $dom = $parser->parse_string(book.xml);
my $root = $dom->documentElement();
my $xpc = XML::LibXML::XPathContext->new($root);

$xpc->registerNs('book', 'http://api.iop.org/Book/1.0/');
$xpc->registerNs('xlink', 'http://www.w3.org/1999/xlink');

foreach my $chapter_node ($xpc->findnodes('/book:bookResource/book:boo
+k/book:meta | /book:bookResource/book:book/book:contents/book:chapter
+'))
{
    foreach my $col(qw/Chapter_Id Chapter_Title Book_Id Book_Publisher
+ Book_Platform Chapter_Doi_Prefix Chapter_Doi Chapter_Id/)
    {
        print $xpc->findvalue($chapter_columns{$col}, $chapter_node);
    }
}
[download]

Have you thought about not printing things if you don't want them printed?

You could also try to make your program remember the current book while descending into the chapters.

I would first find all book:bookResource nodes, and then do a second XPath search relative to each book:bookResource node. This will mean you have to understand how you can walk through an XML tree using XPath.