COMP9311 25T1: Assignment 2
Deadline: Mon. 20:59:59 28th April (Sydney Time)
Note: Please make sure that you always use notations consistent with lecture
notes. Different notations will not be accepted.
Question 1 (12 marks)
Consider a relation R (A, B, C, D, E, G, H, I, J) and its FD set F= {AC -> BDI, DHI-> EJ,
BC ->G, GJ -> H, CEI ->BE, AH->CG}.
Regarding the following questions. Give and justify your answers if the question is
specified.
1) Check if AC→G. Justify your answer. (1 mark)
2) Find all the candidate keys for R. (2 mark)
3) Determine the highest normal form of R with respect to F. Justify your answer.
(2 marks)
4) Find a minimal cover Fm for F. (2 marks)
5) Regarding F, does the decomposition R1 = {ADHJ}, R2 = {CBEH}, R3 = {BGHJ}
of
satisfy the lossless join property? Please justify your answer. (2 marks)
6) Provide a step-by-step lossless decomposition of R into BCNF normal form. (3
marks)
Question 2 (8 marks)
Consider the schedule below. Here, R(*) and W(*) stand for ‘Read’ and ‘Write’,
respectively. T1, T2, T3, T4 and T5 represent five transactions and ti represents a
time slot.
t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 t11 t12
T1
R(A) R(D)
W(A)
W(D)
T2 R(D)
W(D)
T3
R(E)
R(D) W(D)
R(B)
W(B)
T4 R(D)
W(D)
W(C)
T5
W(B)
R(A)
W(A)
Each transaction begins at the time slot of its first operation and commits
right after its last operation (same time slot).
Regarding the following questions. Give and justify your answers.
1) Assume a checkpoint is made between t5 and t6, what should be done to the
five transactions when the crash happens between t9 and t10. (2 marks)
2) Is the transaction schedule conflict serializable? Give the full precedence graph
to justify your answer. (2 marks)
3) Construct a schedule (which is different from above) of these five transactions
which causes deadlock when using two-phase locking protocol. You should
clearly indicate all the locks and the corresponding unlocks in your schedule.
If no such schedule exists, explain why. (4 marks)
Question 3 (6 marks)
Consider the following query:
P1, P2, P3, P4, P3, P4, P1, P2, P4, P5, P2, P1.
(The user is trying to read page 1 from disk, then page 2, page 3, …)
Assume there are 3 buffers in the buffer pool. Regarding the following questions.
Give and justify your answers.
1) Sketch the process of how blocks are replaced in the Least Recently Used (LRU)
policy. (1.5 marks)
2) Sketch the process of how blocks are replaced in the Most Recently Used (MRU)
policy. (1.5 marks)
3) Sketch the process of how blocks are replaced in the First In First Out (FIFO)
policy. (1.5 marks)
4) Between LRU and FIFO policies, which one performs better in the given query?
Why? (1.5 marks)
Assignment Submission
• You are required to submit an electronic version of your answers via
Moodle. While we accept handwritten submissions, please ensure they are
scanned or photographed clearly to ensure legibility.
• We only accept the .pdf format. Please name your files in the following
format: ass2_zID.pdf (e.g., ass2_z5000000.pdf).
Note:
1. If you have problems relating to your submission, please email to
2. If there are issues with Moodle, send your assignment to the above email
with the subject title “ COMP9311 Ass2 Submission”.
Late Submission Penalty
• 5% of the total mark (26 marks) will be deducted for each additional day.
• Submissions that are more than five days late will not be marked.
Plagiarism
The work you submit must be your own work. Submission of work partially or
completely derived from any other person or jointly written with any other person
is not permitted. The penalties for such an offence may include negative marks,
automatic failure of the course and possibly other academic discipline.
All submissions will be checked for plagiarism. The university regards plagiarism
as a form of academic misconduct and has very strict rules. Not knowing the rules
will not be considered a valid excuse when you are caught.
• For UNSW policies, penalties, and information to help avoid plagiarism,
please see: https://student.unsw.edu.au/plagiarism.
• For guidelines in the online ELISE tutorials for all new UNSW students:
https://subjectguides.library.unsw.edu.au/elise/plagiarism.
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