[SOLVED] CS代考 Question 1)

Question 1)
Information Management Prof., Prof. September 2, 2021
Time available 2:00 hours
1. Illustrate the problem of global serializability in a distributed system.

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2. Illustrate the concept of happened before characterizing logical clocks.
3. Fill the attached schema indicating the timestamp associated with each operation of each process. For the exercise, assume to adopt Vector clocks and that all the timestamps are initialized to 0. Operations are denoted with a tick on the line of the corresponding process.
4. Is there any process which does not know anything about another one? Which ones?
Question 2)
1. Illustrate the differences, advantages and disadvantages of using tree-based and bitmap-based indexes for data warehou- ses. In the discussion, also refer to search, insert, and delete operations.
2. Considering the attached table, build the bitmap index for attribute PRODUCT and the bitmap index for attribute CITY. Write the condition operating on bitmap indexes to filter sales for products P1 and P2 sold in Milan or in Rome.
Question 3)
1. Illustrate the apriori property for the efficient identification of frequent itemsets.
2. Illustrate the concepts of support, confidence, and lift in frequent itmeset mining, reporting also the corresponding
3. Fill the attached table with the support and confidence of the association rules that can be obtained from the itemsets in the list.
Itemsets not in the list have frequency equal to 0.
Assume that the overall number of transactions is 50.
For the exercise, consider a minimum threshold for support min sup=0.50 and a minimum threshold for confidence min conf=0.25.
Question 4)
Illustrate the MapReduce computation paradigm, supporting the discussion with examples.

Question 5) only for students who did not attend database course with Prof. Samarati
1. Illustrate the adoption of timestamps for concurrency control, clearly describing the working of the single and multi- version variations.
2. Considering a multiversion timestamp and an object x with initial timestamps RTM(x)=3 e WTM(x)=1. Fill the attached table indicating, for each operation:
(a) if it is accepted;
(b) the version of the object over which it operates;
(c) the new values for RTM(x) and WTM(x);
(d) killed transactions.
RULES FOR THE EXAM
• Cover page: write only name, surname, matriculation number, if you did the exam with prof. Samarati
• White paper: write on each piece of paper name, surname, and matr. number (top left), number of the question (top right) • Use a different piece of paper for each question, for those questions that you decide to skip, draw a line
• Write only on one side of the paper
• Do not write close to the margins: exams will be scanned for correction
• At the end of the time or upon request, deliver your exam (the exams delivered with delay will not be accepted) • Please, order the pieces of paper you are delivering for the exam as follows:
– cover page
– answers (in increasing order of question)

Matr: Question
Surname, Name:
DB with prof. Samarati?: (Y) (N)
Final Mark:
Information Management – September 2, 2021

Matr: Surname, Name: Question 1.3

Matr: Surname, Name: Question 2.2
1 2 3 4 5 6 7 8
Rome Venice

Matr: Surname, Name: Question 3.3 Itemset Frequency
A 30 B 25 C 15
Association Rule
Confidence
Strong? (Y/N)

Matr: Surname, Name: Question 5.2
Killed trans.
read(x, 5)
write(x, 7)
write(x, 15)
read(x, 10)
read(x, 8)
write(x, 9)
write(x, 12)
read(x, 13)

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