Suppose that an airline has a computer system for reserving seats on its planes, which stores data on customer transactions in a relational database.

$($a$)$ Under what circumstances must an exclusive lock be granted by the database management system $($DBMS$)?$

$(2$ marks$)$

$($b$)$ Describe a protocol that the company could use to ensure that schedules are conflict serializable.

$(3$ marks$)$