package Name;
...
__PACKAGE__->set_sql(by_person => q/
    SELECT n.name
    FROM   name n, person_name pn
    WHERE  (n.name_id = pn.firstname
    OR      n.name_id = pn.lastname)
    AND    pn.person = ?
    /);

package Person;
...
sub names {
    my $self = shift;
    Name->search_by_person($self);
}