#!/db01/app/perl/5.6.1/bin/perl

package Test;

use strict;

use Data::Dumper;
use DBI;

sub TIEHASH {
  my($class)=@_;
  my($self)=bless {}, $class;

  # POSITION 1

  $self;
}

sub FETCH {
  my($s,$k,$v)=@_;

  # POSITION 2

  my $store=$s->{STORE}->{$k} ||= {};

  $store->{bar}='baz';

  # POSITION 3
  my $dbh=DBI->connect('dbi:ExampleP:','','')
    or die;

  $store;
}

1;

package main;

use Data::Dumper;

my %h;
tie %h, 'Test';

$h{a}->{'foo'}='bar';

print Dumper $h{a};