#! perl
use strict;
use warnings;
use Data::Dumper;
use XML::Simple;

my $xmldoc  = XMLin("dsys.xml");
my $vendors = $xmldoc->{'Catalog'}->{'Vendors'};
my %vendors = %{ $vendors->{'Vendor'} };
my %unique_vendors;

while (my ($outer_key, $outer_value) = each %vendors)
{
    if (ref($outer_value) eq 'HASH')
    {
        my ($inner_key, $inner_value) = each %$outer_value;

        if ($inner_key eq 'vendorUniqueKey')
        {
            $unique_vendors{$inner_value} = $outer_key;
        }
        else
        {
            warn "Inner key is not 'vendorUniqueKey'";
        }
    }
    else
    {
        warn "Outer value is not a hash reference";
    }
}

print Dumper(\%unique_vendors);

##</code><code>##

$VAR1 = {
          'BETASYS' => 'Beta Systems Software',
          'BMC' => 'BMC Software',
          'ALLENGRP' => 'Allen Systems',
          'AONIX' => 'Aonix North America'
        };