Would you like the data structure like this?

{
  'Entity B' => {
                'Boss' => 'Name',
                'unitnumber' => '2',
                'contactinfo' => {
                                 'URL' => undef,
                                 'email' => undef,
                                 'Telefon' => {
                                              'telnumber' => '456',
                                              'directcall' => '78910',
                                              'code' => '0999'
                                            },
                                 'Address' => {
                                              'zip' => '11111',
                                              'Street' => 'SomeOtherSt
+reet',
                                              'Ort' => 'City',
                                              'Building' => '2'
                                            },
                                 'Fax' => {
                                          'telnumber' => '456',
                                          'directcall' => '10987',
                                          'code' => '0999'
                                        }
                               },
                'products' => {
                              'E5722' => 'few',
                              'C8099' => '522',
                              'F3596' => 'few',
                              'B0765' => '988',
                              'A1136' => '1982',
                              'D3938' => 'few'
                            }
              },
  'Entity A' => {
                'Boss' => 'Name',
                'unitnumber' => '1',
                'contactinfo' => {
...
[download]

use strict;
use XML::Rules;
use Data::Dumper;

my $parser = XML::Rules->new(
    rules => {
        'excerpt' => 'pass no content',
      'Address,Fax,Telefon,contactinfo,products' => 'no content',
      'Boss,Building,Name,Ort,Street,URL,art_code,code,directcall,emai
+l,quantity,quantity_small,telnumber,unitnumber,zip' => 'content',
      'article' => sub {
        if (exists $_[1]->{quantity_small}) {
            return #'%article' =>{
                $_[1]->{art_code} => 'few' # };
        } else {
            return #'%article' => {
                $_[1]->{art_code} => $_[1]->{quantity} #};
        }
      },
      'unit' => 'no content by Name',
    }
);

my $data = $parser->parse(\*DATA);

print Dumper($data);

__DATA__
<excerpt>
<unit>
<unitnumber>1</unitnumber>
...
[download]

The base set of rules was generated by: perl -MData::Dumper -MXML::Rules -e "print Dumper(XML::Rules::inferRulesFromExample( 'c:\temp\excerpt.xml'))"