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# COMP9311 Assignment 2 solved

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## Question 1 (10 marks)

Consider a relation π(π΄, π΅, πΆ,π·, πΈ, πΊ, π»,πΌ,π½,πΎ) and its FD set πΉ = {π΄ β π΅πΆ, πΈ β
π΄π·, π΅π· β πΈ, πΆπΈ β π·π», π» β πΊ, πΈπΌ β π½}.
1) Check if πΆ β π½ β F
+
. (1 marks)
2) Find a minimal cover πΉπ for πΉ. (2 marks)
3) Regarding F, is the decomposition R1 = {π΄π΅πΆπ·πΈ}, R2 = {πΈπΊπ»}, R3 = {πΈπΌπ½πΎ} of π
4) List at least 5 super-keys for π. (2 marks)

5) Is it possible to decompose π into a collection of BCNF relations and ensure the
(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)
3 write(X)
4 write(Z)
6 write(Y)
Transaction
7
8
9 write(X)

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)

## Assignment Submission

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