COMP3311 Database Systems

Transcription

1 The University Of New South Wales Final Exam June 2004 COMP3311 Database Systems Time allowed: 3 hours Total number of questions: 7 Total number of marks: 150 Textbooks, study notes, calculators, mobile phones, etc. are not permitted in this exam. Questions are not worth equal marks. Answer all questions. You can answer the questions in any order. Start each Long Answer Question on a new page in a script book. If you use more than one script book, fill in your details on the front of each book. You may not take this question paper out of the exam. Name: Student#:

2 Part 1: Multiple Choice Question 1 (20 marks) Each of the multiple-choice questions in this part of the exam has four alternatives, only one of which is correct. Once you have chosen the correct alternative, circle your choice in this question book. In this part of the exam, each question is worth 2 marks. There is a penalty of -1 mark for answering a question incorrectly. There is no penalty for not answering a question. a) Which of the following ER diagrams most accurately captures the notion that every employee works in exactly one department? i) Emp WorksIn Dept ii) Emp WorksIn Dept iii) Emp WorksIn Dept iv) Emp WorksIn Dept b) Consider the SQL query on relations R(a, b, c) and S(d, e): select a,e from R,S where c = d and b > 5 Which of the following relational algebra expressions gives a correct translation of this query? i) π (a,e) (σ b>5 (R c=d S)) ii) π (a,e) ((σ (c=d b>5) R) S) iii) π (a) (σ b>5 R) c=d π (e) S iv) π (a) (σ c=d (σ b>5 R π (e) S)) c) Consider the relation R = ABCD and the set F of functional dependencies on its attributes: F = {A B, B C, C D, D A} Which one of the following is a complete set of minimal candidate keys of the relation R? i) {A} ii) {ABCD} iii) {AB, CD} iv) {A, B, C, D} 1

3 d) Which of the relational schemas below is the most accurate translation of the following ER diagram: a c d T b R S e i) T (a, b), R(c), S(d, e) ii) T (a, b, c, d), S(d, e) iii) T (a, b), S(d, e, c, a) iv) T (a, b), R(c, a, d), S(d, e) e) The \dt meta-command in PostgreSQL s psql shell allows a user to... i) define new data types ii) display a list of tables iii) interactively delete tables iv) perform dynamic testing of SQL queries f) For table R(a, b, c) with tuples { (1, a,1), (2, b,1), (3, b,2) } and the PostgreSQL function create or replace function f(int) returns int as select b from R where a=$1 language sql; what is the output of the statement select f(2? i) a ii) b iii) none; there is a syntax error (due to =$ being adjacent) iv) none; PostgreSQL does not support SQL functions that return int values g) If the following sequence of database authorisation operations are executed, what are user U2 s final privileges? U1: grant insert,read,update on A to U2 with grant option U2: grant read on A to U3 with grant option U2: grant insert on A to U4 U1: revoke all on A from U2 restrict i) U2 can insert, read or update tuples in A ii) U2 can insert or update tuples in A iii) U2 can read or insert tuples in A iv) U2 can update tuples in A 2

4 h) In a linear hashed file, the split pointer (sp) indicates the location of i) the next data block to be split ii) the next data block to be filled iii) the last data block that was split iv) the overflow page resulting from the most recent split i) In the two-phase locking protocol for transaction scheduling... i) at most two locks are allowed for any transaction ii) no lock can be released until another transaction requests it iii) locks are acquired in an initial phase, and then released in a final phase iv) all locks from the previous transaction must be released before the next can begin 3

5 Part 2: Long Answer Write your answers to the questions in this part of the exam in the provided script book. Question 2 (15 marks) Consider the following set of requirements to model a large retail organisation with many outlets: Each supplier, product and retailer can be identified by its supplier id (SID), product id (PID) and retailer id (RID) respectively, and each has a name (SNAME, PNAME and RNAME respectively) Every product line has a WEIGHT. For arranging delivery schedules, it is useful to know the LOCATION of suppliers and the LO- CATION of retailers. A supplier can supply many product lines and a product can be supplied by many suppliers. For each product line, a supplier maintains the STOCK level (number of items in its warehouse) and a wholesale PRICE. Every supplier has to supply some product lines. And every product is available from at least one supplier. A retailer sells many product lines and a product can be sold by many retailers. For each product line, a retailer maintains the STOCK level (number of items on its shelves) and a retail PRICE. Every retailer has to sell at least some product. However, not every product line in the suppliers warehouses is necessarily for sale. The organisation arranges delivery of products from suppliers to retailers as shipments from a single supplier to a single retailer. A shipment consists of a number of different product lines, and a number of different product items in each line. We need to record the quantity (QTY) of products in each product line in a shipment. A supplier may send out many shipments to a range of retailers, and a retailer may receive shipments from a range of suppliers. Each shipment has a unique shipment number (SHID), and we need to record when the shipment was PLACED, and when it was finally DELIVERED. Using the information above, draw an ER diagram to model this scenario. Note that you must: a) underline all primary key attributes b) clearly indicate relationship cardinalities c) clearly indicate participation constraints d) use a single, well-recognised ER notation for the entire diagram You can decide names for entities and relations, but, as much as possible, you should use the UPPER- CASE names above for attribute names. 4

6 Question 3 (20 marks) Convert the following ER design for a horse-racing scenario into a relational schema expressed as a collection of PostgreSQL create table statements and a collection of comments that describe all of the assumptions used in determining specific data types for each attribute. Your schema must show all primary key constraints, foreign key constraints and not null constraints suggested by the diagram. You should also include any other common-sense check constraints that you can think of to ensure that attributes contain only sensible values. name colour position name when age Horse Entered Race id d HeldAt Stallion Gelding #children studfee Mare #children RaceCourse id name location For those not familiar with horse/racing terminology: a mare is a female horse a gelding is a male horse that can no longer father children a stallion is a male horse that can father children (for a price... the stud fee ) To get you started on your assumptions, here are some examples: a horse s colour is described by a string such as chestnut or black horses ages are measured in whole years (relative to a generic horses birthday ) the time (field when) for a race includes both a date and time the location of a racecourse can be simply the city name, e.g. there is a racecourse whose name is Randwick which is located in Sydney when a horse enters a race, we record its finishing position as a number (e.g. 1 for first place, 2 for second place, etc. and 0 for scratched ) There is no need to transcribe the above assumptions onto your exam script book, but make sure that you include all others that you make. 5

7 In answering Questions 4-6, make use of the following following PostgreSQL schema to maintain information about the Academy Awards (the Oscars). Assume that the database only contains information about the big four Oscars (Best Actor, Best Actress, Best Director and Best Picture). create table Movie ( id serial, title varchar(100), rating varchar(2) check (rating in ( G, PG, M, MA, R )), runtime integer check (runtime > 0), yearmade integer check (yearmade >= 1926), primary key (id) create table Person ( id serial, name varchar(50), dob date, -- date of birth gender char(1) check (gender in ( M, F )), primary key (id) create table Actor ( person integer references Person(id), movie integer references Movie(id), primary key (person,movie) create table Director ( person integer references Person(id), movie integer references Movie(id), primary key (person,movie) create table Oscar ( id serial, description varchar(20), nwinners integer check (nwinners > 0), primary key (id) create table Winner ( oscar integer references Oscar(id), year integer check (year >= 1927), person integer references Person(id), movie integer references Movie(id), primary key (oscar,year) (continued on next page) 6

8 Most of the fields in the above schema are self-explanatory. The following few may need clarifying: Oscar.nwinners counts how many times this award has been made (note: in some years, there are joint winners, so this value is not simply equal to the number years that the award was presented) Movie.rating gives the standard classifications (e.g. G = General exhibition ) Movie.runtime is the movie s running time in number of minutes for Best Movie winners, Winner.person is the producer (main producer if there are several) for Best Actor or Best Actress winners, Winner.movie is the movie in which they performed for Best Director winners, Winner.movie is the movie that they directed Question 4 (30 marks) Devise SQL queries to provide the answers to each of the following: a) List the names of all Oscar winners and the type of Oscar that each won. (for Best Movie winners, show the producer s name) b) What is the most recent movie for which Tom Hanks won an Oscar? c) How many R-rated (i.e. rating= R ) films have won at least two Oscars? d) Find films which have won all of the big four Oscars; list the names of the films, and the year that they won. e) In which year did Steven Spielberg movies win the largest number of Oscars? f) What is the longest film to have won Best Picture and what was its running time? g) Determine the average ages of the Best Actress winners and of the Best Actor winners when they won their awards. h) In what years, since the awards began, was there no Best Director award made? (You can assume that there was a Best Picture award presented in every year since the awards began). You may define auxiliary views if they make it easier to describe the query. Question 5 (25 marks) Write PLpgSQL trigger functions to ensure that the following assertions are maintained on the database for insert and delete operations (we will ignore update for the purposes of this exercise): a) Oscar.nWinners is consistent with the number of times that particular Oscar is mentioned in the Winner table b) a Best Actress Oscar can never be awarded to a male actor c) for a Best Director Oscar, the director must have already been recorded as the director of that movie, and the movie must have been made either in the year of the award or in the previous year For each of these, you should also provide a create trigger statement to set up the trigger function. In each case, you should state whether the trigger is either a before or after trigger, and explain why you chose to implement it that way. If you need to terminate an operation due to inappropriate data values, raise an exception with a suitable message to indicate what the problem is. 7

9 Question 6 (20 marks) The following partially complete PHP script implements a search facility that allows users to type in a keyword and see a list of all academy awards where the keyword appears either in the movie title or the person s name associated with that award. (Note that if multiple keywords are entered into the text input box, only the first will be used.) <?... the PHP code for part (a) goes here...?> <html> <head><title>academy Awards Search</title></head> <body> <h2>academy Awards Search</h2> <form method="post"> Search: <input type="text" name="word" value="<?=$word?>"> <input type="submit" value="search!"> </form> <?... the PHP code for part (b) goes here...?> </body> </html> Your tasks for this question a) Write PHP that collects the CGI parameter word and, if it exists, uses it to ask a query that fetches a collection of tuples representing Oscar winners that contain the word either in the movie title or the person s name. The result tuples from this query should be of the form: (NameOfAward, Y ear, NameOfP erson, MovieT itle) The results of this query should be stored in a PHP array assigned to a variable called $results. You can assume that the database is called oscars and that you have direct access to it without needing to specify a DB username or password. Your code should check whether the database is accessible and whether there are errors in invoking the query. If either of those conditions fails, you should call a function called dberror() that will terminate the script and produce a suitable HTML-format message for the user. You may not make use of the getvalues() function from Assignment 3 in answering this question, even if you happen to remember what its arguments look like. b) Write PHP code that will take the $results array produced in the first part of the question, and display it as an HTML table, with one tuple per row, with the columns in the order specified in the the first part. If there was no query executed in the first part, the script should simply display nothing. If a query was invoked, but no results were returned, it should display No results. You may assume the existence of a function called tableheadings() which takes an array of strings and returns a single string containing the HTML for a row of column headings. You may also assume the existence of a function called tablerow(), which takes an array of strings and returns a single string containing the HTML for a table row containing the input strings, one per column. 8

10 Question 7 (20 marks) a) For the relational schema Employee(eno, fname, lname, dept, salary) Department(dno, dname, manager, budget) translate the following relational algebra expressions into SQL queries: i) π fname,lname,salary (σ dept=5 (Employee)) ii) π lname,dname (Employee (eno=manager) Department) b) What is the result of the relational algebra operation A/B for the relations: A = x y l m n l l m n B = y l m n c) Consider the relation: Students(sid, fname, lname, street,...) which contains 8,000 records and is stored in a heap file. Assume that: pages are 4KB (4096 bytes), page-addresses are 4 bytes long, sid is 8 bytes long, Student records are 100 bytes long, and slot directories within data pages are 64 bytes long. i) How many Student records fit onto a block? ii) How many blocks are required to store the entire file? iii) How many blocks would a dense index on sid need? iv) Based on the index, what is the cost (in page reads) of evaluating the query: select * from Students where sid= Note: you can present the results to this question as an unevaluated formula, so you don t need to do all of the arithmetic. d) Consider the following schedule for two transactions on shared data objects X and Y: R 1 (X), R 1 (Y), W 1 (X), R 2 (Y), W 3 (Y), W 1 (X), R 2 (Y) Draw its serializability graph and determine its serializability. 9