Question

Which of the following schedules is conflict serializable?

a) S': R1(X), R2(x), W1(Y), R3(Y), R2(Y), W2(x), R3(W), W3(y), R4(w), R4(2)
b) S': R1(X), R2(x), W1(Y), R3(Y), R2(Y), W2(x), R3(W), W3(y), R4(w), R4(2), I
c) S': R1(X), R2(x), W1(Y), R3(Y), R2(Y), W2(x), R3(W), W3(y), R4(w), R4(2), WI(Z)
d) None of the above

Answer 1

Conflict serializability determines if a database schedule can be rearranged into a serial schedule without conflicts. The question's schedules cannot be definitively considered conflict serializable without constructing precedence graphs and checking for cycles. Therefore, the correct answer is 'd) None of the above'.

Step-by-step explanation:

The question asks which of the given schedules is conflict serializable. Conflict serializability is an aspect of concurrency control in databases that determines if a schedule (sequence of read and write operations) can be rearranged without any conflicts into a serial schedule (one where transactions are ordered one after the other). To determine if a schedule is conflict serializable, we must analyze the precedence graph of the schedule for cycles.

Looking at the schedules provided:

1. Schedule 'a' has read-write and write-read conflicts between transactions T1, T2, and T3 which makes it difficult to serialize without further information.
2. Schedule 'b' has an extra character 'I' that seems to be a typo and is not relevant to the analysis of the schedule.
3. Schedule 'c' has the operation WI(Z) which is a write operation by T1 on a variable Z not previously read or written by other transactions listed in this schedule. This does not by itself cause any conflicts with the existing set of operations, but we need to check for conflicts between other operations.

Based on the information provided, and given that the schedules may contain typos or irrelevant parts, it appears there are potential conflicts in schedules 'a' and 'b', while schedule 'c' might be conflict serializable if there are no other conflicts. However, without constructing the precedence graph for each schedule and analyzing it thoroughly for cycles, we cannot definitively say which schedule is conflict serializable. As such, the correct answer would be 'd) None of the above' unless we are provided with clearer schedules or additional information.