Nandini,
When ever a record is to be modified it better follow the sequence lock-->read-->modify-->unlock
your present implementation may not support add and delete functionality. If FBNS decides to extend your application to give this functionality to certain users, add and delete methods should lock the entire database before modifying the it. Also, as some people have suggested locking the entire database could be done just before shutting the server down.
This is just my interpretation of the instructions.
Regards
badari
SCJP, SCJD, SCBCD, SCEA, IBM 665