Package My::Hosts;
use base qw(My::Class::DBI::Subclass);
__PACKAGE__->table('hosts');
__PACKAGE__->columns(Primary => qw(ID));
__PACKAGE__->columns(Essential => qw(name IPAddress location OS));
__PACKAGE__->has_many('mailservers', 'My::MailServers', 'host');
__PACKAGE__->has_many('webservers', 'My::WebServers', 'host');

# has_many also defines a column in the foreign class: 
# in this case webserver->host
# which returns the relevant Hosts object when called.

Package My::MailServers;
use base qw(My::Class::DBI::Subclass);
__PACKAGE__->table('mailservers');
__PACKAGE__->columns(Primary => qw(ID));
__PACKAGE__->columns(Essential => qw(MTA version));

Package My::WebServers;
use base qw(My::Class::DBI::Subclass);
__PACKAGE__->table('webservers');
__PACKAGE__->columns(Primary => qw(ID));
__PACKAGE__->columns(Essential => qw(httpd version CGI mod_perl port https));