ETH Zurich Spring Semester Systems Group Lecturer(s): Gustavo Alonso, Ce Zhang Date: August 19, Exam. Questions

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1 Data Modelling and Databases (DMDB) ETH Zurich Spring Semester 2017 Systems Group Lecturer(s): Gustavo Alonso, Ce Zhang Date: August 19, 2017 Assistant(s): Claude Barthels, Eleftherios Sidirourgos, Last update: Februar 05, 2018 Eliza Wszola, Ingo Müller, Kaan Kara, Renato Marroquín, Zsolt István Exam Rules (please read carefully) You have 120 minutes for the exam. Write the answers on the stack of papers with the title answer sheets. Write your name and Legi number on the cover page of the answer sheets. Please write your Legi number on all other pages of the answer sheets. Use blue or black ink, DO NOT USE red ink. DO NOT USE pencils. Write as clearly as possible and cross out everything that you do not consider to be part of your solution. Answers can be given in either English or German. Hand in your answer sheet. Do not hand in the sheets with the questions. You may keep the question sheets. Remarks Most questions are designed such that the fastest way to solve them is to solve the problem rather than looking at the answers and try to determine which one is correct. We expect it to be slower to try out all combinations of questions and solutions in order to find the ones that match. Do not answer questions at random as wrong answers give negative points. If you do not know the answer, leave it blank.

2 1 Entity-Relationship Model (10 points) Consider the following entity-relationship model: FamilyName ReaderNr ReturnDate Shelf Position Firstname Reader N Borrows M Copy CopyNr City Birthdate N Available 1 Catname 1 ISBN Contains Category N InCat M Book PubYear N N Title Publisher 1 Publishes NumPages Author Pubname Pubcity Solve the following subproblems. (a) (5 points) Given a particular concept (entity or attribute) of Type 1, how many different instances of concepts of Type 2 can it be associated with? In the table on the answer sheet, mark with a checkmark ( ) the widest range that applies. Example: If A is associated with exactly one entity of type B, the corresponding row will look as follows. Type 1 Type 2 A B number of entities of Type 2 exactly 1 at most 1 at least 1 any number (incl. zero) Grading: Each correct answer gives 0.5 point. Each incorrect answer gives point.

3 (b) (2 points) On the answer sheet, mark with a checkmark ( ) whether each of the given statements is true or false. (A) A category can contain itself. (B) If we need to express that a book must have exactly 2 copies, we can do it provided we use a different notation. (C) The model allows a reader to borrow a copy of a non-existent book. (D) Each entity must have exactly one key attribute. Grading: Each correct answer gives 0.5 point. Each incorrect answer gives point. (c) (1 point) Suppose that each book has a unique title. We replace Book s title attribute with a "hastitle" relationship: 1 1 Book Available hastitle Copy Title What is the effect of this change? Pick one answer and mark it on the answer sheet. A. Aside from enforcing title uniqueness, it has no effect. B. A book previously had exactly one title. Now, it has at most one. C. A book previously could have at most one title. Now, it must have exactly one. D. A book previously had exactly one title. Now, it can have arbitrarily many titles. E. A book previously could have at most one title. Now, it can have arbitrarily many titles. (d) (2 points) Suppose we add a new entity set Librarian and connect it to the Borrows relationship in the following way: N M Reader Borrows Copy 1 Librarian On the answer sheet, mark with a checkmark ( ) whether each of the given statements is true or false. Grading: Each correct answer gives 0.5 point. Each incorrect answer gives point.

4 2 Relational Model (8 points) Consider the ER models 1 to 4 and the relational models (a) to (j) given below. For each ER model, specify the letter of the relational model that represents it correctly in the table on the answer sheet, or write none in the space if there is none that represents it. Grading: 2 points for each correct answer, -1 point for each wrong answer. B 1 1 C N c B 1 N C 1 c b R S s b R S s r N D 1 d r N D N d ER model 1 ER model 2 B 1 1 C 1 c B 1 N C c b r R N S D N s d b r R N is_a D s d ER model 3 ER model 4 (a) B(b) R(b,c,d,r), extra key: b,d S(c,d,s) (b) B(b) C(c) D(c,d,s) R(b,c,c,d,r) (c) B(b) C(c) D(c,d,s) R(b,c,d,r), extra key: b,d (d) B(b) D(c,d) R(b,c,d,r), extra key: b,d S(c,d,s) (e) B(b) C(c) D(c,d,s) R(b,c,d,r) (f) B(b) C(c) D(c,d,s) R(b,c,c,r) (g) B(b) C(c) D(c,d,s) R(b,c,c,d,r), extra key: b,d,c (h) B(b) C(c) D(c,d,s) R(b,c,d,r), extra key: b,d (i) B(b) C(c) D(c,d,s) R(b,c,d,r) (j) B(b) C(c,d,s) D(d) R(b,c,d,r), b,d extra key:

5 3 Relational Algebra (15 points) (a) (6 points) Consider the two following relations (A and B). A = W X 1 a 2 c 2 f 3 a 9 b B = X Y Z a 9 3 b 2 1 b 3 1 g 3 0 f 2 0 Consider the following three join queries (Q 1, Q 2, Q 3 ). Q1: A B Q2: A B Q3: A W =Y B For each of the tuples in the answer sheet, mark if the tuple is part of the result of the queries with a checkmark ( ). If a tuple is not part of the result set of a query, place a cross (X) in the corresponding field. Note: The result set can contain additional tuples that are not listed in the answer sheet. Grading: Each correct answer gives 0.25 points. Each incorrect answer gives points. (b) (6 points) Consider the following relations (C, D, E). C = X Y 1 a 2 c 2 f 3 a D = Y c b a b d Z a b f c a E = Z X a 3 b 1 f 2 c 2 For each of the relational algebra expressions listed in the answer sheet, calculate the size (cardinality) of the result set. Grading: Each correct answer gives 1 point. Each incorrect answer gives -0.5 points.

6 (c) (3 points) Consider the following relations modelling a library management system. Reader ( RDNR, Surname, Firstname, City, BirthYear ) Book ( ISBN, Title, Author, NoPages, PubYear, PublisherName ) Publisher ( PublisherName, PublisherCity ) Category ( CategoryName, Description ) Copy ( ISBN, CopyNumber, Shelf, Position ) Loan ( ReaderNr, ISBN, Copy, ReturnDate ) BookCategory ( ISBN, CategoryName ) Consider the following questions: Q1: Which readers (first and last name) from Zurich have read books that have been published before their birth year? Q2: Which books (title) have never been read by a reader from Zurich? Q3: Which publishers (name) offer at least one book not belonging to the category Switzerland? Consider the following queries: A: Π F irstname,surname (σ P uby ear<birthy ear (Reader Loan Book)) B: Π T itle (Book Π Book (σ City= Zurich (Reader) Loan Copy Book)) C: Π F irstname,surname (σ City= Zurich (σ P uby ear<birthy ear(reader Loan Copy))) D: Π P ublishername (Book Π Book (σ CategoryName= Switzerland (BookCategory Book))) E: Π T itle (Book Π Book (σ City= Zurich (Reader Loan Book))) F: Π P ublishername (Π Book (σ CategoryName<> Switzerland (BookCategory Book))) In the answer sheet, mark which query answers which question by placing a a checkmark ( ) in the corresponding field, otherwise leave the field blank. If a query does not answer any question, place a checkmark ( ) in the right-most column in the answer grid. If a question is answered by multiple relational algebra queries, mark all of them. Grading: Each correct answer gives 1 point.

7 4 SQL I (12 points) Suppose we create the following database tables. No additional constraints are imposed. CREATE TABLE Store( id INT NOT NULL, name VARCHAR(30) NOT NULL, city VARCHAR(30) NOT NULL, PRIMARY KEY (id) ); CREATE TABLE Product( id INT NOT NULL, name VARCHAR(30) NOT NULL, supplier VARCHAR(30) NOT NULL, release_year INT, PRIMARY KEY (id) ); CREATE TABLE Available( store_id INT NOT NULL, product_id INT NOT NULL, available_since_year INT NOT NULL, quantity INT NOT NULL, PRIMARY KEY (store_id, product_id) ); Suppose we insert some values to the tables so that we have: Store: Product: Available: id name city 1 Alices Lucerne 2 Black Market Zug 3 CXHJ Aarau 4 Do-It Winterthur id name supplier release_year 1 Mark I IBM ENIAC United States Army Analytical Engine Babbage NULL store_id product_id available_since_year quantity

8 (a) (5 points) How many rows do the following queries return? Grading: Each correct answer gives 1 point. Each incorrect answer gives -0.5 points. 1. SELECT product_id FROM Available WHERE store_id = 1 UNION SELECT product_id FROM Available WHERE store_id = 2; 2. SELECT product_id FROM Available WHERE store_id = 1 INTERSECT SELECT product_id FROM Available WHERE store_id = 2; 3. SELECT product_id, SUM(quantity) FROM Available WHERE quantity > 30 GROUP BY product_id; 4. SELECT product_id, SUM(quantity) FROM Available GROUP BY product_id HAVING SUM (quantity) > 30; 5. SELECT id, ( CASE WHEN release_year = 1946 THEN 'new edition' WHEN release_year = 1944 THEN 'old edition' END ) AS comment FROM Product; (b) (2 points) What are the values returned by the following statement? (SELECT id FROM Product WHERE release_year > 1945 UNION ALL SELECT id FROM Product WHERE release_year <= 1946) ORDER BY id; A. 1, 2 B. 1, 2, 3 C. 1, 2, 2 D. 1, 2, 2, 3, 3 E. 1, 1, 2, 2 F. 1, 1, 2, 2, 3, 3

9 (c) (2 1 / 2 points) Using the given building blocks (A-H), fill the gaps in the query so that it returns results corresponding to the problem description. On the answer sheet, write the letter corresponding to a selected building block next to the number of each gap. Problem: Find stores in which you can buy particular rare products. A product is rare if its total quantity on the market is lower than 60. Resulting rows should consist of store name, product name and supplier. SELECT Product.name, Product.supplier, Store.name FROM Product JOIN Available ON Product.id = Available.product_id JOIN Store ON Store.id = Available.store_id WHERE Product.id 1 ( SELECT 2 GROUP BY product_id ); A. IN B. < C. = D. id FROM Product E. product_id FROM Available F. HAVING SUM(quantity) G. WHERE SUM(quantity) H. EXCEPT (d) (2 1 / 2 points) Repeat the same task for the following problem: Select the names and release years of all products and order the results by release years. If no release year is available, the lowest product s "available_since_year" in the Available table should be used. SELECT name, (CASE 1 ( SELECT 2 FROM Available WHERE 3 = id ) 4 release_year END ) AS release_year FROM Product ORDER BY release_year; A. WHEN release_year = NULL THEN B. WHEN release_year IS NULL THEN C. ELSE D. ELSE THEN E. MIN(available_since_year) F. available_since_year G. product_id H. store_id

10 5 SQL II (5 points) Consider the following relations: Reader ( RDNR, Surname, Firstname, City, BirthYear ) Book ( ISBN, Title, Author, NoPages, PubYear, PublisherName ) Publisher ( PublisherName, PublisherCity ) Category ( CategoryName, BelongsTo ) Copy ( ISBN, CopyNumber, Shelf, Position ) Loan ( ReaderNr, ISBN, Copy, ReturnDate ) BookCategory ( ISBN, CategoryName ) (a) (2 1 / 2 points) Consider a SQL database with the above relations, where all attributes are specified to be NOT NULL. Given the following query template that should list all readers that loaned books of the following categories ROMANCE, DRAMA or MYSTERY. SELECT RDNR, Surname FROM Reader, Loan, BookCategory WHERE predicate ; For each of the following predicates, say whether it produces the desired result if used in the template: (A) Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND (BookCategory.CategoryName = 'ROMANCE' OR BookCategory.CategoryName = 'DRAMA' OR BookCategory.CategoryName = 'MYSTERY') (B) Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND (BookCategory.CategoryName = 'ROMANCE' AND BookCategory.CategoryName = 'DRAMA' AND BookCategory.CategoryName = 'MYSTERY') (C) (Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND BookCategory.CategoryName = 'ROMANCE') OR (Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND BookCategory.CategoryName = 'DRAMA') OR (Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND BookCategory.CategoryName = 'MYSTERY') (D) Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND BookCategory.CategoryName = 'ROMANCE' OR BookCategory.CategoryName = 'DRAMA' OR BookCategory.CategoryName = 'MYSTERY' (E) (Reader.RDNR = Loan.ReaderNr AND BookCategory.ISBN = Loan.ISBN AND BookCategory.CategoryName = 'ROMANCE') OR BookCategory.CategoryName = 'DRAMA' OR BookCategory.CategoryName = 'MYSTERY' Grading: 0.5 points for each correct answer points for each incorrect answer.

11 (b) (2 1 / 2 points) Consider the following query that retrieves a single reader among the youngest readers who returned a book the longest time ago. SELECT Firstname, Surname, ReturnDate FROM Reader, Loan WHERE Reader.RDNR = Loan.ReaderNr ORDER BY Reader.BirthYear DESC, Loan.ReturnDate ASC LIMIT 1; For each of the following statements, say whether they are TRUE or FALSE. (A) The query does not produce the desired result because it does not have a JOIN clause. (B) The query would be wrong if it had an ORDER clause with only one of the two attributes. (C) The LIMIT clause is not needed as the query returns all the needed tuples in the right order. (D) Both relations Reader and Loan are needed to relate the readers with the loans they have made. (E) If two readers born on the same year returned a book on the same day, the query would return incorrect results. Grading: 0.5 points for each correct answer points for each incorrect answer.

12 6 SQL III (7 1 / 2 points) Consider the following relations: Reader ( RDNR, Surname, Firstname, City, BirthYear ) Book ( ISBN, Title, Author, NoPages, PubYear, PublisherName ) Publisher ( PublisherName, PublisherCity ) Category ( CategoryName, BelongsTo ) Copy ( ISBN, CopyNumber, Shelf, Position ) Loan ( ReaderNr, ISBN, Copy, ReturnDate ) BookCategory ( ISBN, CategoryName ) Consider a SQL database with the above relations, where all attributes are specified to be NOT NULL. Now consider the following seven queries: (Q1) SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR WHERE Loan.ISBN IN ( SELECT ISBN FROM Copy GROUP BY ISBN HAVING COUNT(CopyNumber) = 13 ) (Q2) SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR WHERE Loan.ISBN IN ( SELECT ISBN FROM Copy WHERE CopyNumber = 13 ) (Q3) WITH ( SELECT ISBN, COUNT(*) AS cnt FROM Copy GROUP BY ISBN ) AS Interm SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR JOIN Copy ON Copy.ISBN = Loan.ISBN JOIN Interm ON Copy.ISBN = Interm.ISBN WHERE Interm.cnt = 13 (Q4) SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR WHERE Loan.ISBN IN ( SELECT DISTINCT ISBN FROM Copy WHERE CopyNumber = 13 ) (Q5) WITH ( SELECT Book.ISBN AS ISBN, COUNT(Title) AS cnt, MAX(CopyNumber) AS maxcn FROM Copy JOIN Book ON Book.ISBN = Copy.ISBN GROUP BY ISBN ORDER BY cnt DESC ) AS Interm SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR JOIN Copy ON Copy.ISBN = Loan.ISBN JOIN Interm ON Copy.ISBN = Interm.ISBN WHERE Interm.cnt = 13

13 (Q6) WITH ( SELECT Book.ISBN AS ISBN, COUNT(Title) AS cnt, MAX(CopyNumber) AS maxcn FROM Copy JOIN Book ON Book.ISBN = Copy.ISBN GROUP BY ISBN ORDER BY cnt DESC LIMIT 13 ) AS Interm SELECT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR JOIN Copy ON Copy.ISBN = Loan.ISBN JOIN Interm ON Copy.ISBN = Interm.ISBN (Q7) SELECT DISTINCT ReaderNR FROM Reader JOIN Loan ON Reader.RDNR = Loan.ReaderNR WHERE Loan.ISBN IN ( SELECT ISBN FROM Copy GROUP BY ISBN HAVING COUNT(CopyNumber) = 13 ) Some of these queries solve the same task and return identical results. Using the table on the answer sheet, determine which queries are equivalent by defining equivalence classes consisting of all queries that return identical results on any database instance. Grading: Partial points for every correct equivalence. 0 points if any false equivalence is specified.

14 7 Integrity Constraints (12 points) (a) (3 points) Consider the following ER model. Which relational database schema represents this model accurately? Complete the correpsonding DML statements on the answer sheet. /^E E d E (b) (6 points) Consider the following schema: CREATE TABLE Reader ( ReaderNr INT PRIMARY KEY, FamilyName VARCHAR(20) NOT NULL, FirstName VARCHAR(20) NOT NULL ); CREATE TABLE Copy ( CopyNr INT NOT NULL PRIMARY KEY, Position INT NOT NULL ); CREATE TABLE Borrows ( ReaderNr INT NOT NULL, CopyNr INT NOT NULL, PRIMARY KEY(ReaderNr, CopyNr), constraint fk_reader FOREIGN KEY(ReaderNr) ON DELETE RESTRICT ON UPDATE CASCADE, constraint fk_copy FOREIGN KEY(CopyNr) ON DELETE NO ACTION ON UPDATE RESTRICT ); Initially, the relations contain the following entries: Copy = Reader = ReaderNr FamilyName FirstName 1 Turing Alan 2 Shannon Claude 3 Hamming Richard CopyNr Position Borrows = ReaderNr CopyNr 1 3 The answer sheet contains sequences of queries that are executed on these relations one after each other. Each sequence starts with the initial state of the database. For each sequence, answer the corresponding question by filling in the table on the answer sheet. Sequence (i): How many tuples are in each relation after executing the queries? Sequence (ii): How many tuples are in each relation after executing the queries? Sequence (iii): Can the queries by executed (yes/no for each query)? Sequence (iv): Can the queries by executed (yes/no for each query)? Grading 0.5 points for each correct answer (table cell), -0.5 points for each incorrect answer.

15 (c) (3 points) For each of the following statements, determine whether it is true or false by placing a checkmark ( ) in the corresponding cell of the table on the answer sheet. (A) An ON UPDATE SET NULL constraint ensures that an update on the referenced entry will cause the foreign key that references the updated entry to be set to NULL. (B) An ON UPDATE CASCADE constraint specified for an attribute in a table may lead to changing attributes in other tables. (C) An ON DELETE RESTRICT constraint ensures that an entry in the referenced table cannot be deleted, if a reference to it exists. Grading: 1 point for each correct line, -1 for each wrong line.

16 8 Normal Forms (12 points) (a) Consider the relation R(A, B, C, D, E) with the following three sets of functional dependencies F 1, F 2, F 3. F 1 F 2 F 3 A C C E A B C DE BD AE AC DE B AE A BC AD C i. (3 points) For each set of functional dependencies, determine all the candidate keys of the relation R. Grading: Each correct answer gives 1 point. ii. (3 points) For each set of functional dependencies, determine the highest normal form the relation R is in. Grading: Each correct answer gives 1 point. (b) Consider the following relation with its set of functional dependencies. Book ( ISBN, Title, Author, NoPages, PubYear, PublisherName, PublisherCity ) ISBN Title, Author, NoPages, PubYear, PublisherName PublisherName PublisherCity i. (1 point) What is the highest normal form the relation is in? What is the problematic functional dependency that prevents the relation from being in a higher normal form? A. ISBN Title, Author, NoPages, PubYear, PublisherName B. PublisherName PublisherCity ii. (1 point) Propose a lossless decomposition of the relation that brings the relation into a higher normal form. Mark all keys of the relations. iii. (1 point) Proof that the proposed decomposition is lossless. (c) Consider the relation R(A, B, C, D, E) with the following set of functional dependencies. A BC DE BC C D i. (1 point) Find the minimum basis of the set of functional dependencies. A. DE BC, C D B. A BC, E B, C D C. A BC, E BC, C D D. A BC, DE BC E. The given set of functional dependencies is minimal. F. None of the above. ii. (1 point) Find the correct decomposition of R given each set of functional dependencies according to the synthesis algorithm. iii. (1 point) Which is the highest normal form that the synthesis algorithm guarantees the resulting relation(s) to be in?

17 9 Join Processing (7 points) Given are three relations R, S and T that already reside in memory. Their cardinalities are as follows: R =12,000 S =90,000 T =1,000,000 We have a query Q twj that requires joining the three tables together. The estimate of the pairwise join sizes for the join predicates used in this query are: R S =2,000 R T =11,000 T S =3,000 (a) (1 point) How many possible join orders are there for these three relations? Grading: 1 point for correct answer. (b) (3 points) If we choose to use only block nested loop joins for Q twj and take the number of comparisons as cost, what is the optimal join order? Write down the cost of each join in that particular ordering. Grading: 3 points if both the order and the calculations are correct. (c) (3 points) Assume we use only the canonical hash join algorithm to execute the join and all intermediary data fits in memory. We take the number of hash table accesses (inserts or lookups) as the cost of a join. What is the optimal join order in this case? Write down the cost of each join in that particular ordering. Grading: 3 points if both the order and the calculations are correct.

18 10 Transactions (13 1 / 2 points) Notation used in this exercise: b i - Begin of transaction i. r i (A) - Transaction i reads data object A. w i (A) - Transaction i writes to data object A. c i - Transaction i commits successfully. a i - Transaction i aborts or is aborted. (a) (4 1 / 2 points) For each of the given histories below, draw a serializability graph on the answer sheet and indicate if it is serializable. i. r 2 (A) r 3 (B) w 3 (B) r 2 (B) w 2 (A) r 1 (A) w 1 (A) r 3 (A) c 3 c 2 c 1 ii. r 1 (A) r 2 (B) w 1 (A) w 2 (A) r 3 (A) w 3 (A) c 1 c 2 c 3 iii. r 1 (A) w 1 (A) r 2 (A) w 2 (A) w 2 (B) r 1 (B) c 2 c 1 (b) (9 points) For each of the following histories, find the strictest recoverability class (not recoverable, recoverable, avoid-cascading aborts, strict) and indicate if it is possible under strict 2-phase locking (S2PL) and snapshot isolation (SI), respectively. Write the name of the recoverability class in the table on the answer sheet and write Yes or No indicating if the history is possible. 1. History: b 1 r 1 (A) b 2 r 2 (A) r 2 (B) w 2 (A) w 1 (B) c 1 c 2 2. History: b 1 r 1 (A) b 2 w 1 (A) c 1 r 2 (A) w 2 (A) c 2 3. History: b 1 b 2 r 1 (A) r 2 (C) w 1 (B) w 1 (A) c 1 w 2 (A) c 2 4. History: b 1 w 1 (A) c 1 b 2 r 2 (A) b 3 r 3 (A) w 2 (B) w 3 (C) c 2 c 3 5. History: b 1 r 1 (A) w 1 (A) b 2 r 2 (A) c 2 b 3 r 3 (B) c 3 c 1 6. History: b 1 w 1 (B) b 2 w 2 (B) c 1 r 2 (A) r 2 (B) c 2 Grading: 0.5 for every correct answer (table cell), -0.5 for each incorrect answer.

19 11 Two-Phase Commit (18 points) Consider a distributed transactional system with one coordinator C and two participants P 1 and P 2. The coordinator also acts as participant. We describe the execution of the Two- Phase Commit Protocol among these nodes as a sequence of the following types of events. The first letter of each event indicates the node takes the action, the second entry the action, and the third letter the recipient of the action where applicable. Types of events that can only take place at the coordinator (C): C, VoteRequest, P i = C sends a vote request to participant P i C, ReceiveVote, P i = C receives a vote from participant P i C, SendCommit, P i = C sends a Commit decision to node P i C, SendAbort, P i = C sends an Abort decision to participant P i Types of events that can only take place at the participants (P i ): P i, ReceiveVoteRequest, C = P i receives a vote request from C P i, ReceiveDecision, C = P i receives the global decision from C P i, VoteAbort, C = P i sends an Abort vote to C P i, VoteCommit, C = P i sends an Abort vote to C Types of events that can take place at any node (X {C, P 1, P 2 }): X, Fail = X fails X, Recover = X finishes recovery X, Abort = X (locally) notifies the rest of the system that the global decision is to abort X, Commit = X (locally) notifies the rest of the system that the global decision is to commit X, Timeout, Y = times out waiting for a message from Y, Y {C, P 1, P 2 } You can abbreviate the action component of events by the capital letters of that action. For example, you can write RVR for ReceiveVoteRequest or F for Fail. (a) (5 points) Assume that P 1 fails before it is contacted by the coordinator with a VoteRequest and it does not Recover. Assume also that P 2 votes Commit when asked. Construct a sequence of events describing a correct and complete execution of the Two-Phase Commit Protocol for this situation. Write your solution on the answer sheet. (b) (5 points) Construct a sequence of events describing a correct and complete execution of the Two-Phase Commit Protocol where one participant is uncertain and therefore not allowed to Commit because some other site s decision has been to Abort. Write your solution on the answer sheet.

20 (c) (8 points) Assume that we add the following operation to the repertoire of possible events taking place at any node X, X {C, P 1, P 2 }: X, log action = X writes an entry about action into its persistent log Assume that the protocol produces the strict minimum of number of log events needed to recover from failures. For each of the following statements, state whether it is true or false by checking the corresponding box in the table on the answer sheet. (A) C, log StartProtocol must take place before any C, VoteRequest, P i. (B) Each C, VoteRequest, P i must be preceeded by C, log VoteRequest, P i. (C) Each C, VoteRequest, P i must be followed by C, log VoteRequest, P i. (D) Each P i, VoteCommit, C must be preceeded by P i, log VoteCommit. (E) Each P i, VoteCommit, C must be followed by P i, log VoteCommit. (F) Each C, SendCommit, P i must be preceeded by C, log ReceiveVote, P i. (G) Each C, SendCommit, P i must be followed by C, log ReceiveVote, P i. (H) C, Commit can only take place after a C, ReceiveVote, P i for each P i. (I) Each X, Commit must be preceeded by X, log Commit. (J) Each X, Commit must be followed by X, log Commit. (K) After P i, log VoteCommit, it is possible to observe P i, Abort. (L) After P i, log VoteAbort, it is possible to observe P i, Commit. (M) If P i, log VoteCommit was the last log event before P i, Fail, P i can deduce the outcome of the transaction without the help of any other site after P i, Recover. (N) If P i, log VoteAbort was the last log event before P i, Fail, P i can deduce the outcome of the transaction without the help of any other site after P i, Recover. (O) If P i, log Commit was the last log event before P i, Fail, P i can deduce the outcome of the transaction without the help of any other site after P i, Recover. (P) If P i, log Abort was the last log event before P i, Fail, P i can deduce the outcome of the transaction without the help of any other site after P i, Recover. Grading: 0.5 points for each correct line for each wrong line.

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25 Data Modelling and Databases (DMDB) ETH Zurich Spring Semester 2017 Systems Group Lecturer(s): Gustavo Alonso, Ce Zhang Date: August 19, 2017 Assistant(s): Claude Barthels, Eleftherios Sidirourgos, Last update: Februar 05, 2018 Eliza Wszola, Ingo Müller, Kaan Kara, Renato Marroquín, Zsolt István Exam Answer Sheets Name: Legi-Nr: Question: Total Points: / / Score: Reminders Write all your answers on this stack of papers ( answer sheets ). Write your name and Legi number on the cover page of the answer sheets. Please write your Legi number on all other answer sheets. Do not separate the individual sheets of this stack. If there are pages missing, you will not receive any points for these pages. Hand in this stack of answer sheets.

26 Legi-Nr: 1 Entity-Relationship Model Question 1.a: Type 1 Type 2 number of entities of Type 2 exactly 1 at most 1 at least 1 any number (incl. zero) Book Book Book Book Book Category Copy ISBN NumPages Publisher Category Copy Publisher ISBN NumPages Book Book Book Book Book Question 1.b: Statement TRUE FALSE Statement (A) Statement (B) Statement (C) Statement (D) Question 1.c: A B C D E Question 1.d: Statement TRUE FALSE 1. A particular reader can borrow from many librarians. 2. A particular copy can be borrowed from many librarians. 3. A particular copy can be borrowed by only one reader. 4. A particular copy can be borrowed by a particular reader only from one librarian. 2 Relational Model Question 2: ER model ER model 1 ER model 2 ER model 3 ER model 4 Relational Model

27 Legi-Nr: 3 Relational Algebra Question 3.a: Tuple [A.W, A.X, B.X, B.Y, B.Z] Q 1 Q 2 Q 3 [-, -, b, 2, 1] [1, a, -, -, -] [3, a, b, 3, 1] [9, b, b, 2, 1] [2, c, -, -, -] [2, f, f, 2, 0] [1, a, a, 9, 3] [2, c, f, 2, 0] Question 3.b: Query Result Set Size C D E (C D) E C σ X>1 (E) C ρ Z Y (E) D Π Z (E) Π Z (D) Π Z (E) Question 3.c: Question A B C D E F No matching query Q1 Q2 Q3 4 SQL I Question 4.a: query rows Question 4.b: A B C D E F

28 Legi-Nr: Question 4.c: gap block Question 4.d: gap block SQL II Question 5.a: Predicate produces desired result yes no (A) (B) (C) (D) (E) Question 5.b: Statement true false (A) (B) (C) (D) (E)

29 Legi-Nr: 6 SQL III Question 6: Equivalence class List of equivalent queries C1 C2 C3 C4 C5 C6 C7 7 Integrity Constraints Question 7.a: CREATE TABLE Book ( ); CREATE TABLE Copy ( );

30 Legi-Nr: Question 7.b: (i) (ii) Query INSERT INTO Reader VALUES (1, Huffman, David); DELETE FROM Reader WHERE ReaderNr = 1; Query INSERT INTO Borrows VALUES (2, 5); DELETE FROM Copy WHERE CopyNr = 5; Number of tuples in Reader Copy Borrows Number of tuples in Reader Copy Borrows (iii) (iv) Query INSERT INTO Reader VALUES (4, Hopper, Grace); UPDATE Reader SET ReaderNr = 7 WHERE FamilyName = Turing ; UPDATE Copy SET CopyNr = 4 WHERE Position = 8001; Query DELETE FROM Reader WHERE ReaderNr = 3; UPDATE Copy SET Position = 3002 WHERE CopyNr = 3; DELETE FROM Borrows WHERE ReaderNr = 1; Executable? Executable? Question 7.c: Statement True False Statement (A) Statement (B) Statement (C) 8 Normal Forms Question 8.a.i: Functional Dep. Candidate Keys F 1 F 2 F 3

31 Legi-Nr: Question 8.a.ii: Functional Dep. No NF 1NF 2NF 3NF BCNF F 1 F 2 F 3 Question 8.b.i: No NF 1NF 2NF 3NF BCNF 4NF Problematic functional dependency: A B Question 8.b.ii: Question 8.b.iii: Question 8.c.i: A B C D E F Question 8.c.ii: Question 8.c.iii: No NF 1NF 2NF 3NF BCNF 4NF 9 Join Processing Question 9.a:

32 Legi-Nr: Question 9.b: Question 9.c: 10 Transactions Question 10.a.i: Question 10.a.ii: Question 10.a.iii: Question 10.b: History Recoverablity S2PL SI 1. History 2. History 3. History 4. History 5. History 6. History

33 Legi-Nr: 11 Two-Phase Commit Question 11.a: Question 11.b:

34 Legi-Nr: Question 11.c: Statement true false Statement (A) Statement (B) Statement (C) Statement (D) Statement (E) Statement (F) Statement (G) Statement (H) Statement (I) Statement (J) Statement (K) Statement (L) Statement (M) Statement (N) Statement (O) Statement (P)