welcome to the lock/unlock loop.
Venkata it is actually a sequence lock.
once you read the data you and show it to the user, till that point it is fine. but after that when u try to book the tickets for the user how do u have the gurantee that the records shown to the user are same and consistent with the database.
so for tha u start a sequence lockin mechanism and read the data and modify it.
i hope i have cleared your doubt
and the information was a descent eye opener for you