package SalesOrder;
use Class::MethodMaker
   new_hash_init => 'new',
   get_set       => [qw(Customer OrderDate SONumber Items)],
;

package Customer;
use Class::MethodMaker
   new_hash_init => 'new',
   get_set       => [qw(CustName CustNumber Street City State PostCode)],
;

package Item;
use Class::MethodMaker
   new_hash_init => 'new',
   get_set       => [qw(ItemNumber Part Quantity)],
;

package Part;
use Class::MethodMaker
   new_hash_init => 'new',
   get_set       => [qw(PartNumber Description Price)],
;

package main;
use strict;
use warnings;
use Data::Dumper;
use XML::Simple;

my $xml   = XMLin(\*DATA, KeyAttr => []);
my $items = [ map Item->new(Part => Part->new(delete $_->{Part}), %$_), @{$xml->{Item}} ];
delete $xml->{Item};

my $sales_order = SalesOrder->new(
    Customer => Customer->new(%{ delete $xml->{Customer} }),
    Items    => $items,
    %$xml,
);

print Dumper $sales_order;

__DATA__
<SalesOrder SONumber="12345">
  <Customer CustNumber="543">
     <CustName>ABC Industries</CustName>
     <Street>123 Main St.</Street>
     <City>Chicago</City>
     <State>IL</State>
     <PostCode>60609</PostCode>
  </Customer>
  <OrderDate>981215</OrderDate>
  <Item ItemNumber="1">
     <Part PartNumber="123">
        <Description>Turkey wrench: Stainless steel, one-piece construction, lifetime guarantee.</Description>
        <Price>9.95</Price>
     </Part>
     <Quantity>10</Quantity>
  </Item>
  <Item ItemNumber="2">
     <Part PartNumber="456">
        <Description>Stuffing separator: Aluminum, one-year guarantee.</Description>
        <Price>13.27</Price>
     </Part>
     <Quantity>5</Quantity>
  </Item>
</SalesOrder>