I just suddenly think of a question. For the network mode, if there are 2 users on 2 different machines, connects to the same server, and perform the update task, what should I do? According to the instructions in the assignment, this case is not mention. Still, I think only 1 user (FCFS-based) should update the record, and the other requests are rejected. But, how should I handle this case? Get a lock on item X, check before update, if it is already non-empty, then throws an AlreadyBookedException? Thanks a lot.