COMP9311 Assignment 2 solved

Description

Question 1 (10 marks)

Consider a relation 𝑅(𝐴, 𝐵, 𝐶,𝐷, 𝐸, 𝐺, 𝐻,𝐼,𝐽,𝐾) and its FD set 𝐹 = {𝐴 → 𝐵𝐶, 𝐸 →
𝐴𝐷, 𝐵𝐷 → 𝐸, 𝐶𝐸 → 𝐷𝐻, 𝐻 → 𝐺, 𝐸𝐼 → 𝐽}.
1) Check if 𝐶 → 𝐽 ∈ F
+
. (1 marks)
2) Find a minimal cover 𝐹𝑚 for 𝐹. (2 marks)
3) Regarding F, is the decomposition R1 = {𝐴𝐵𝐶𝐷𝐸}, R2 = {𝐸𝐺𝐻}, R3 = {𝐸𝐼𝐽𝐾} of 𝑅
lossless-join? Please justify your answer. (2 marks)
4) List at least 5 super-keys for 𝑅. (2 marks)

5) Is it possible to decompose 𝑅 into a collection of BCNF relations and ensure the
decomposition is dependency-preserving and lossless-join? Please justify your answers.
(3 marks)

Question 2 (6 marks)

Following is the schedule A for transactions T1, T2, and T3:
Schedule A
Time T1 T2 T3
1 write(X)
2 read(Z)
3 write(X)
4 write(Z)
5 read(Z)
6 write(Y)
Transaction
7
8
9 write(X)
10 read(Y)

1) Assume that the system crashes at time 8, what should be done to recover the system? (3
marks)
2) Assume a checkpoint is made at time 7, what should be done to the three transactions
when the crash happens at time 8? (3 marks)
Note: We assume a transaction will be committed immediately after all the read/write
operations of it are done.

Question 3 (4 marks)

Give and justify the answers regarding the following problems:
1) Construct a scenario that First in First Out (FIFO) buffer replacement policy is better
than Most Recently Used (MRU) buffer replacement policy. (2 marks)
2) Construct a scenario that First in First Out (FIFO) buffer replacement policy is better
than Least Recently Used (LRU) buffer replacement policy. (2 marks)

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