my %books;
my $twig= new XML::Twig(
    twig_handlers => { book => \&books }
);
$twig->parse($xmlStr);
print Dumper(\%books);
exit;

sub books {
    my ($twig, $book) = @_;
    my $id = $book->att('id');
    $books{$id}{'author'        } = $book->first_child('author'      )->text();
    $books{$id}{'title'         } = $book->first_child('title'       )->text();
    $books{$id}{'genre'         } = $book->first_child('genre'       )->text();
    $books{$id}{'price'         } = $book->first_child('price'       )->text();
    $books{$id}{'publish_date'  } = $book->first_child('publish_date')->text();
}  

##</code><code>##

use strict;
use warnings;
use XML::Twig;
use Data::Dumper;

my $xmlStr = <<XML;
<?xml version="1.0"?>
<catalog>
   <book id="bk101">
      <author>Gambardella, Matthew</author>
      <title>XML Developer's Guide</title>
      <genre>Computer</genre>
      <price>44.95</price>
      <publish_date>2000-10-01</publish_date>
      <description>An in-depth look at creating applications 
      with XML.</description>
   </book>
   <book id="bk102">
      <author>Ralls, Kim</author>
      <title>Midnight Rain</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-12-16</publish_date>
      <description>A former architect battles corporate zombies, 
      an evil sorceress, and her own childhood to become queen 
      of the world.</description>
   </book>
   <book id="bk103">
      <author>Corets, Eva</author>
      <title>Maeve Ascendant</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2000-11-17</publish_date>
      <description>After the collapse of a nanotechnology 
      society in England, the young survivors lay the 
      foundation for a new society.</description>
   </book>
   <book id="bk104">
      <author>Corets, Eva</author>
      <title>Oberon's Legacy</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-03-10</publish_date>
      <description>In post-apocalypse England, the mysterious 
      agent known only as Oberon helps to create a new life 
      for the inhabitants of London. Sequel to Maeve 
      Ascendant.</description>
   </book>
   <book id="bk105">
      <author>Corets, Eva</author>
      <title>The Sundered Grail</title>
      <genre>Fantasy</genre>
      <price>5.95</price>
      <publish_date>2001-09-10</publish_date>
      <description>The two daughters of Maeve, half-sisters, 
      battle one another for control of England. Sequel to 
      Oberon's Legacy.</description>
   </book>
   <book id="bk106">
      <author>Randall, Cynthia</author>
      <title>Lover Birds</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-09-02</publish_date>
      <description>When Carla meets Paul at an ornithology 
      conference, tempers fly as feathers get ruffled.</description>
   </book>
   <book id="bk107">
      <author>Thurman, Paula</author>
      <title>Splish Splash</title>
      <genre>Romance</genre>
      <price>4.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>A deep sea diver finds true love twenty 
      thousand leagues beneath the sea.</description>
   </book>
   <book id="bk108">
      <author>Knorr, Stefan</author>
      <title>Creepy Crawlies</title>
      <genre>Horror</genre>
      <price>4.95</price>
      <publish_date>2000-12-06</publish_date>
      <description>An anthology of horror stories about roaches,
      centipedes, scorpions  and other insects.</description>
   </book>
   <book id="bk109">
      <author>Kress, Peter</author>
      <title>Paradox Lost</title>
      <genre>Science Fiction</genre>
      <price>6.95</price>
      <publish_date>2000-11-02</publish_date>
      <description>After an inadvertant trip through a Heisenberg
      Uncertainty Device, James Salway discovers the problems 
      of being quantum.</description>
   </book>
   <book id="bk110">
      <author>O'Brien, Tim</author>
      <title>Microsoft .NET: The Programming Bible</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-09</publish_date>
      <description>Microsoft's .NET initiative is explored in 
      detail in this deep programmer's reference.</description>
   </book>
   <book id="bk111">
      <author>O'Brien, Tim</author>
      <title>MSXML3: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>36.95</price>
      <publish_date>2000-12-01</publish_date>
      <description>The Microsoft MSXML3 parser is covered in 
      detail, with attention to XML DOM interfaces, XSLT processing, 
      SAX and more.</description>
   </book>
   <book id="bk112">
      <author>Galos, Mike</author>
      <title>Visual Studio 7: A Comprehensive Guide</title>
      <genre>Computer</genre>
      <price>49.95</price>
      <publish_date>2001-04-16</publish_date>
      <description>Microsoft Visual Studio 7 is explored in depth,
      looking at how Visual Basic, Visual C++, C#, and ASP+ are 
      integrated into a comprehensive development 
      environment.</description>
   </book>
</catalog>
XML

my %books;
my $twig= new XML::Twig(
    twig_handlers => { book => \&books }
);
$twig->parse($xmlStr);
print Dumper(\%books);
exit;

sub books {
    my ($twig, $book) = @_;
    my $id = $book->att('id');
    $books{$id}{'author'        } = $book->first_child('author'      )->text();
    $books{$id}{'title'         } = $book->first_child('title'       )->text();
    $books{$id}{'genre'         } = $book->first_child('genre'       )->text();
    $books{$id}{'price'         } = $book->first_child('price'       )->text();
    $books{$id}{'publish_date'  } = $book->first_child('publish_date')->text();
}  

##</code><code>##

$VAR1 = {
          'bk111' => {
                     'publish_date' => '2000-12-01',
                     'price' => '36.95',
                     'title' => 'MSXML3: A Comprehensive Guide',
                     'author' => 'O\'Brien, Tim',
                     'genre' => 'Computer'
                   },
          'bk108' => {
                     'publish_date' => '2000-12-06',
                     'price' => '4.95',
                     'title' => 'Creepy Crawlies',
                     'author' => 'Knorr, Stefan',
                     'genre' => 'Horror'
                   },
          'bk105' => {
                     'publish_date' => '2001-09-10',
                     'price' => '5.95',
                     'title' => 'The Sundered Grail',
                     'author' => 'Corets, Eva',
                     'genre' => 'Fantasy'
                   },
          'bk102' => {
                     'publish_date' => '2000-12-16',
                     'price' => '5.95',
                     'title' => 'Midnight Rain',
                     'author' => 'Ralls, Kim',
                     'genre' => 'Fantasy'
                   },
          'bk112' => {
                     'publish_date' => '2001-04-16',
                     'price' => '49.95',
                     'title' => 'Visual Studio 7: A Comprehensive Guide',
                     'author' => 'Galos, Mike',
                     'genre' => 'Computer'
                   },
          'bk106' => {
                     'publish_date' => '2000-09-02',
                     'price' => '4.95',
                     'title' => 'Lover Birds',
                     'author' => 'Randall, Cynthia',
                     'genre' => 'Romance'
                   },
          'bk107' => {
                     'publish_date' => '2000-11-02',
                     'price' => '4.95',
                     'title' => 'Splish Splash',
                     'author' => 'Thurman, Paula',
                     'genre' => 'Romance'
                   },
          'bk103' => {
                     'publish_date' => '2000-11-17',
                     'price' => '5.95',
                     'title' => 'Maeve Ascendant',
                     'author' => 'Corets, Eva',
                     'genre' => 'Fantasy'
                   },
          'bk104' => {
                     'publish_date' => '2001-03-10',
                     'price' => '5.95',
                     'title' => 'Oberon\'s Legacy',
                     'author' => 'Corets, Eva',
                     'genre' => 'Fantasy'
                   },
          'bk109' => {
                     'publish_date' => '2000-11-02',
                     'price' => '6.95',
                     'title' => 'Paradox Lost',
                     'author' => 'Kress, Peter',
                     'genre' => 'Science Fiction'
                   },
          'bk101' => {
                     'publish_date' => '2000-10-01',
                     'price' => '44.95',
                     'title' => 'XML Developer\'s Guide',
                     'author' => 'Gambardella, Matthew',
                     'genre' => 'Computer'
                   },
          'bk110' => {
                     'publish_date' => '2000-12-09',
                     'price' => '36.95',
                     'title' => 'Microsoft .NET: The Programming Bible',
                     'author' => 'O\'Brien, Tim',
                     'genre' => 'Computer'
                   }
        };