...
  <inventors type="array">
    <inventor>
      <city>Aston Clinton</city>
      <name>Andy Barth</name>
      <number type="integer">1</number>
      <country>GB</country>
      <upper-name>ANDY BARTH</upper-name>
    </inventor>
    <inventor>
      <city>Aylesbury</city>
      <name>Daniele Dall'Acqua</name>
      <number type="integer">2</number>
      <country>GB</country>
      <upper-name>DANIELE DALL'ACQUA</upper-name>
    </inventor>
    <inventor>
      <city>Calne</city>
      <name>Nigel Drew</name>
      <number type="integer">3</number>
      <country>GB</country>
      <upper-name>NIGEL DREW</upper-name>
    </inventor>
  </inventors>
...

##</code><code>##

my $xml_to_hash = XMLin($xml_file,
  #ForceArray => 0,
  #KeyAttr    => {},
 );

##</code><code>##

$VAR1 = {
  'inventors' => {
     'inventor' => {
        'Nigel Drew' => {
            'country' => 'GB',
            'city' => 'Calne',
            'number' => {
            'content' => '3',
            'type' => 'integer'
          },
          'upper-name' => 'NIGEL DREW'
        },
        'Daniele Dall\'Acqua' => {
           'country' => 'GB',
           'city' => 'Aylesbury',
           'number' => {
              'content' => '2',
              'type' => 'integer'
             },
           'upper-name' => 'DANIELE DALL\'ACQUA'
        },
        'Andy Barth' => {
           'country' => 'GB',
           'city' => 'Aston Clinton',
           'number' => {
              'content' => '1',
              'type' => 'integer'
             },
           'upper-name' => 'ANDY BARTH'
        }
     },
    'type' => 'array'
  },

##</code><code>##

$VAR1 = {
  'inventors' => [
	{
	  'inventor' => [
	  {
	    'country' => ['GB'],
	    'city' => ['Aston Clinton'],
	    'upper-name' => ['ANDY BARTH'],
	    'number' => [{'content' => '1', 'type' => 'integer'}],
	    'name' => ['Andy Barth']
	  },
	  {
	    'country' => ['GB'],
	    'city' => ['Aylesbury'],
	    'upper-name' => ['DANIELE DALL\'ACQUA'],
	    'number' => [{'content' => '2', 'type' => 'integer'}],
	    'name' => ['Daniele Dall\'Acqua']
	  },
	  {
	    'country' => ['GB'],
	    'city' => ['Calne'],
	    'upper-name' => ['NIGEL DREW'],
	    'number' => [{'content' => '3', 'type' => 'integer'}],
	    'name' => ['Nigel Drew']
	  }
      ],
      'type' => 'array'
    }
   ], ...

##</code><code>##

foreach my $inventors(%{$xml_to_hash->{inventors}}){
  if ($inventors->{inventor}->{number}->{content} == 1){
     print $inventors->{inventor};
     }
  }

##</code><code>##

foreach my $inventor(%{$xml_to_hash->{inventors}->{inventor}}){
   if ($inventor->{number}->{content} == 1){
      print $inventor;
      }
   }