I find the kind of relationship that Jackie and Donna have,to be quite simular to that of Facts Of Life characters Blair Warner and Jo Polniciak{pardon me if I mispelled Jo's last name}.Blair and Jo were famous for their constant exchange of wisecracks and cut-up remarks.Some of you may agree that Donna and Jackie have the same kind of cut-up relationship.Not to mention,Donna is rather cool and tomboyish like Jo,just as Jackie seems quite like Blair.I suppose it's a common sitcom form used frequently.:D