1. PROJECT Serial_no, Manufacturer, Sale_price( SELECT Name='Jane Doe' (SALESPERSON NATURAL JOIN salesperson_id = salesperson_id(CAR serial_no = serial_no)
2. PROJECT Serial_no, Model(SELECT(CAR NATURAL JOIN OPTION) - SELECT(CAR NATURAL JOIN serial_no = serial_no OPTION))
3. Keeps all tuples in SALESPERSON regardless of whether or not they were matched based on the join criteria. Pads all non-matches with NULL.
4. PROJECT Model(SELECT date "1/11/15" AND serial_no=serial_no(SALE X CAR)