##
use XML::LibXML;
my $parser = XML::LibXML->new();
my $doc = $parser->parse_file("book_service.xml");
my $xpc = XML::LibXML::XPathContext->new($doc->documentElement());
foreach my $book_node ($xpc->findnodes('/book:bookResource/book:book/book:meta'))
{
foreach $book_element ('./*/@isbn[@type="epub"]')
{
print $book_node->findvalue($book_element);
}
}