Hospi$-$Helper is an online software system that can be used by hotels and inns to manage reservations.

Customers and hotel sales representatives can use the system to check room availability and room price. They can also make, modify, and cancel reservations. When a reservation is made the customer's bank verifies the payment. When it is canceled the customer's bank refunds the payment. Housekeepers can use the system to update the ready status of rooms $($clean$,$ ready to be occupied$).$ Front desk attendants can use the system to check guests into and out of rooms.

Up to three rooms can be booked on a single reservation. A reservation has check$-$in and check$-$out dates. It has a status $($Canceled$,$ Confirmed, Paid, and in$-$Progress$).$ It also has an associated customer. A customer is a guest who is at least $21$ years$-$old with an associated credit card that will be used to pay for the reservation and incidentals.

A credit card must realize the following interface operations: getAccountNumber, getExpirationDate, getSecurityCode, and charge $($which returns false if the charge fails for some reason$).$ Currently, only Visa and MasterCard realize this interface.

A guest has an associated room and a unique key access code. A guest is also associated with first and last name, address, phone number, and a date of birth.

A room has a room number, a nightly rate, is either smoking or non$-$smoking, is or isn't occupied, and is or isn't ready $($i$.$e$.,$ clean$).$ There are several types of rooms: Queen, Double Queen, and King. A room is associated with zero or more reservations that it is booked by$.$ It has zero to three guests.