[SOLVED] CS代考 Question 1)

Question 1)
Information Management
July 21, 2020
Time available 2:00 hours (1:30 hours for students who do not answer to question 5)

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1. Illustrate the concept of happened before characterizing logical clocks.
2. Describe the differences between Lamport clocks and Vector clocks.
3. Fill the attached schema indicating the timestamp associated with each operation of each process. For the exercise, assume to adopt Lamport clocks and that all the timestamps are initialized to 0. Operations are denoted with a tick on the line of the corresponding process.
P1 :t1,t2,… P2 :t1,t2,… P3 :t1,t2,…
Question 2)
1. What is a bitmap index? Clearly explain its advantages and disadvantages.
2. Build the bitmap index for attribute PRODUCT and the bitmap index for attribute MONTH.
Write the condition operating on bitmap indexes to filter sales for product P1 sold in January and February.
1 2 3 4 5 6
jan feb jan jan mar feb

Question 3)
1. Illustrate the apriori property for the efficient identification of frequent itemsets.
2. Considering the table attached and assuming min sup=0.75, identify all the frequent itemsets using apriori algorithm.
2 A,B,C,D 3 A,B,D,E 4 B,C,D
Question 4)
Illustrate the main differences between a traditional relational database and a NoSQL database.
Question 5) only for students who did not attend database course with Prof. Samarati
1. Briefly illustrate ACID properties. 2. Given the following log:
DUMP, B(T1), B(T2), U(T1,O1,B1,A1), I(T2,O2,A2), B(T3), D(T1,O3,B3), A(T1), B(T4), CK(. . . ), U(T3,O4,B4,A4), D(T4,O5,B5), I(T3,O6,A6), B(T5), I(T5,O7,A7), C(T3), B(T6), D(T6,O8,B8), C(T4), A(T2), U(T5,O9,B9,A9) FAILURE
(a) write, for each checkpoint record, active transactions;
(b) illustrate in the details the steps of a warm restart to recover from failure.

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