No storage has been allocated here  for  TOTAL_PRICE.   Instead,  VAX
  DATATRIEVE  uses  the  virtual  expression "UNIT_PRICE * QUANTITY" to
  calculate the value of TOTAL_PRICE at run time.

  TOTAL_PRICE            DATATYPE IS VIRTUAL FIELD
                         COMPUTED BY DATATRIEVE AS
                             "UNIT_PRICE * QUANTITY".