#!/usr/bin/env perl

use strict;
use warnings;

use Inline::Files;
use XML::Simple qw{:strict};

my %xml_hash = (Data => {});
my $xml_data = $xml_hash{Data};
my (%db1, %db2);

while (<DB1>) {
    my ($root, $table, $key) = split;
    push @{$db1{$root}{$table}}, $key;
    $xml_data->{$root}{$table}{NEW1}{KEY} = [$key];
}

while (<DB2>) {
    my ($root, $table, $key) = split;
    push @{$db2{$root}{$table}}, $key;
    $xml_data->{$root}{$table}{NEW2}{KEY} = [$key];
}

while (<DIFF>) {
    my ($root, $table, $key, $col, $old, $new)
        = map { $_ eq '<null>' ? '' : $_ } split;
    $xml_data->{$root}{$table}{NEW1}{KEY} = $db1{$root}{$table}
        if exists $db1{$root}{$table};
    $xml_data->{$root}{$table}{NEW2}{KEY} = $db2{$root}{$table}
        if exists $db2{$root}{$table};
    $xml_data->{$root}{$table}{MODIFIED}{KEY}{$key}{$col}{oldvalue} = [$old];
    $xml_data->{$root}{$table}{MODIFIED}{KEY}{$key}{$col}{newvalue} = [$new];
}

print XMLout(\%xml_hash, KeepRoot => 1, KeyAttr => {KEY => 'name'});

__DIFF__
EMPLOYEE      EMPLOYEE      XYZ      TITLE    <null>      Mr    
EMPLOYEE      EMPDETAILS    DEF      CITY    California  New York    
CUSTOMER      CUSTOMER      ABC      CAPTION  Regular    Premium   
__DB1__
EMPLOYEE    EMPLOYEE    NEW_EMPLOYEE_1
EMPLOYEE    EMPLOYEE    NEW_EMPLOYEE_9
EMPLOYEE    EMPDETAILS  NEW_EMPLOYEE1-DETAILS
EMPLOYEE    EMPDETAILS  NEW_EMPLOYEE9-DETAILS
EMPLOYEE    EMPDETAILS  NEW_EMPLOYEE16-DETAILS
IN_DB1_ONLY IN_DB1_ONLY IN_DB1_ONLY
IN_DB1+DB2  IN_DB1+DB2  IN_DB1+DB2
__DB2__
EMPLOYEE    EMPLOYEE    NEW_EMPLOYEE_6
EMPLOYEE    EMPDETAILS  NEW_EMPLOYEE6-DETAILS
CUSTOMER    CUSTOMER    NEW_CUSTOMER
IN_DB2_ONLY IN_DB2_ONLY IN_DB2_ONLY
IN_DB1+DB2  IN_DB1+DB2  IN_DB1+DB2

##</code><code>##

$ pm_xml_db_diff2.pl
<Data>
  <CUSTOMER>
    <CUSTOMER>
      <MODIFIED>
        <KEY name="ABC">
          <CAPTION>
            <newvalue>Premium</newvalue>
            <oldvalue>Regular</oldvalue>
          </CAPTION>
        </KEY>
      </MODIFIED>
      <NEW2>
        <KEY>NEW_CUSTOMER</KEY>
      </NEW2>
    </CUSTOMER>
  </CUSTOMER>
  <EMPLOYEE>
    <EMPDETAILS>
      <MODIFIED>
        <KEY name="DEF">
          <CITY>
            <newvalue>New</newvalue>
            <oldvalue>California</oldvalue>
          </CITY>
        </KEY>
      </MODIFIED>
      <NEW1>
        <KEY>NEW_EMPLOYEE1-DETAILS</KEY>
        <KEY>NEW_EMPLOYEE9-DETAILS</KEY>
        <KEY>NEW_EMPLOYEE16-DETAILS</KEY>
      </NEW1>
      <NEW2>
        <KEY>NEW_EMPLOYEE6-DETAILS</KEY>
      </NEW2>
    </EMPDETAILS>
    <EMPLOYEE>
      <MODIFIED>
        <KEY name="XYZ">
          <TITLE>
            <newvalue>Mr</newvalue>
            <oldvalue></oldvalue>
          </TITLE>
        </KEY>
      </MODIFIED>
      <NEW1>
        <KEY>NEW_EMPLOYEE_1</KEY>
        <KEY>NEW_EMPLOYEE_9</KEY>
      </NEW1>
      <NEW2>
        <KEY>NEW_EMPLOYEE_6</KEY>
      </NEW2>
    </EMPLOYEE>
  </EMPLOYEE>
  <IN_DB1+DB2>
    <IN_DB1+DB2>
      <NEW1>
        <KEY>IN_DB1+DB2</KEY>
      </NEW1>
      <NEW2>
        <KEY>IN_DB1+DB2</KEY>
      </NEW2>
    </IN_DB1+DB2>
  </IN_DB1+DB2>
  <IN_DB1_ONLY>
    <IN_DB1_ONLY>
      <NEW1>
        <KEY>IN_DB1_ONLY</KEY>
      </NEW1>
    </IN_DB1_ONLY>
  </IN_DB1_ONLY>
  <IN_DB2_ONLY>
    <IN_DB2_ONLY>
      <NEW2>
        <KEY>IN_DB2_ONLY</KEY>
      </NEW2>
    </IN_DB2_ONLY>
  </IN_DB2_ONLY>
</Data>