#!/usr/bin/perl

my $foo_datum;
my $unique_id;
my $bar_number;
my $good_info;

my $xml_source = XMLin($xml_file, forcearray => 
   [ qw (thing foo bar bazs) ], keyattr =>[ ]);

foreach my $thing_loop (@{$xml_source->{'things'}->{'thing'}} ) {
   $unique_id = $thing_loop->{'unique_identifier'};   
   
   foreach my $foo_loop (@{$thing_loop->{'foos'}->{'foo'}} ) {
      $foo_datum = $foo_loop->{'foo_datum'};
   }
   
   foreach my $bar_loop (@{$thing_loop->{'bars'}->{'bar'}} ) {
      $bar_number = $bar_loop->{'bar_number'};
      $good_info = $bar_loop->{'good'}->{'good_info'};
   }
   
   # Compare $foo_datum, $bar_number and $good_info with what's in
   # the database.
   
}