Databases System. Exercise 18.1.1. A transaction T1, executed by an airline-reservation system, performs the following steps:

i. The customer is queried for a desired flight time and cities. Information about the desired flights is located in database elements (perhaps disk blocks) A and B, which the system retrieves from disk.

ii. The customer is told about the options, and selects a flight whose data, including the number of reservations for that flight is in B. A reservation on that flight is made for the customer.

iii. The customer selects a seat for the flight; seat data for the flight is in database element C.

iv. The system gets the customers credit-card number and appends the bill for the flight to a list of bills in database element D.

v. The customers phone and flight data is added to another list on database element E for a fax to be sent confirming the flight.

The Question: Express transaction T₁ as a sequence of r and w actions.