use XML::Twig;
my $xml = <DATA>;
my $twig = new XML::Twig (
  TwigHandlers => { 
    'volume' => sub { print "Volume: " . @_->text . "\n" }, 
    'issue' => sub { print "Issue: " . @_->text . "\n" },
    'year' => sub { print "Year: " . @_->text . "\n" },
  }
);
$twig->parse($xml);
__DATA__
<data>
<volume>4</volume>
<issue>12</issue>
<year>2003</year>
</data>