package FinancialTransaction;
# You may ask, "if this is an abstract class, why does it have a constructor"?
# Simple: I don't want to rewrite the same code for every subclass. That's
# a much bigger source of potential bugs than the risk of some numptie who didn't
# read the docs trying to instanciate the superclass.
# If you're a real pedant, add a runtime check, as with getall().
sub new { my ($proto, $id) = @_;
    my $this = { id => $id };
    bless $this, (ref($proto) or $proto);
}

sub getall { my ($proto) = @_;
    my $class = (ref($proto) or $proto);
    die "Subclasses only" if $class eq "FinancialTransaction";
    my $dnasample = bless({}, $class);
    # Get @ids from somewhere... (arguments? database? file?)
    # eg. the result of "SELECT id FROM $class"
    foreach (@ids) { $_ = $dnasample->new($_); }
    \@ids;
}

# General accessor/mutator
sub _am { my ($this, $field, $val) = @_;
    if(defined $val) {
        # Execute "UPDATE ".$this->TABLE." SET $field = ? WHERE id=?"
        # For bindings $val and $this->{'id'}
    } else {
        # Return the result of a similar SELECT statement
    }
}

package Deposit;
use base qw(FinancialTransaction);
use constant TABLE => 'DEPOSIT';
sub someattribute { $this->_am('someattribute', @_); }

package Withdrawl;
use base qw(FinancialTransaction);
use constant TABLE => 'WITHDRAWL';
sub someotherattribute { $this->_am('someotherattribute', @_); }

You can now do my $deposits = Deposit->getall;, and my $withdrawls = Withdrawl->getall;, but you haven't had to redefine what is essentially the same constructor in multiple places. This is a royal PITA to try to do in Java (believe me, I made the mistake of trying in my E-Business coursework), and basically forces you to use the Factory pattern instead, which means even more classes to maintain.