1 (10) 2 (8) 3 (12) 4 (14) 5 (6) Total (50)

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1 Student number: Signature: UNIVERSITY OF VICTORIA Faculty of Engineering Department of Computer Science CSC 370 (Database Systems) Instructor: Daniel M. German Midterm Oct 21, 2004 Duration: 60 minutes This is a closed-book exam. You are only allowed one, hand written, letter-size sheet of paper. This examination paper consists of 13 pages and 5 sections. Please bring any discrepancy to the attention of an invigilator. The number in parenthesis at the start of each question is the number of points the question is worth. Answer all questions. Please write your answers clearly. For instructor s use: 1 (10) 2 (8) 3 (12) 4 (14) 5 (6) Total (50) Score Page 1 of 13

2 For this exam, consider the following schema and instances of the relations. Feel free to remove this page from the exam. Attributes with an empty value should be assumed to be NULL. Students(sid: integer, sname: string, age: integer, gpa: real) Primary Key: sid sid sname age gpa 1 Storey Damian Hoffman Courses(cid: string, cname: string, department: 5) Primary Key: cid cid cname department CSC-370 Managing my phone book CS HIST-320 History of geeks HIST CSC-450 Social Networks CS CHEM-100 Baking doughnuts CHEM Enrolled(sid: integer, cid: string, grade: integer) Primary Key: (sid,cid) Foreign Key: sid references Students Foreign Key: cid references Courses sid cid grade 1 CSC CSC CSC CSC CSC HIST CSC 370 PAGE 2

3 1. Database Concepts (a) [2] In relational theory, what is a domain? (b) [2] For a given relation, if PK is the set of attributes in its primary key, and CK is the set of attributes of one of its candidate keys, such that PK CK, can the following statement ever be true? Explain. (PK CK) CSC 370 PAGE 3

4 (c) [2] Consider a relation with the following schema: Students(sid, sname) With candidate key sid. The relation contains n tuples (n > 0). What can you say about the cardinality of π sid (Students)? (d) [2] What is the result of the following expression: NOT(NULL = NULL) (e) [2] In relational theory relations cannot have duplicates, but in practice DBMS allow duplicates. Briefly explain why. CSC 370 PAGE 4

5 2. Database Design (a) [5] The company ACME buys parts from different suppliers. Each part has as attributes a partid (guaranted to be unique), and a part name. Suppliers are identified by a supplierid (guaranteed to be unique), and supplier name. A given part is supplied by exactly one supplier. Any given supplier should supply zero or more parts. Draw the ER diagram that describes this situation. CSC 370 PAGE 5

6 (b) [3] Translate your diagram to a collection of CREATE TABLE statements, including any constraints you can possible enforce. CSC 370 PAGE 6

7 3. Relational Algebra and Calculus (a) [3] Write a tuple relational calculus expression that corresponds to the query: what is the sid of students whose name is Craig. (b) [3] Write a relational algebra expression that computes the sid and sname of all the students taking all the courses offered by the department CS. CSC 370 PAGE 7

8 (c) [6] Consider the relations R(A : a, B : b, C : c) and S(A : a, C : c, D : d, E : e). Which of the following expressions are legal and if they are not, explain why. i. R S ii. π B (R) π B (R) iii. R S CSC 370 PAGE 8

9 4. Writing SQL queries Answer the following questions using the schema in page 2. (a) [3] Find the sid, sname of all the students who are older than 19 years old. (b) [3] Find the sid of the students who are not taking any course. CSC 370 PAGE 9

10 (c) [4] Find the sid, sname of every student who is registered in exactly one course. (d) [4] For each course that: has at least 2 students enrolled, OR is taught by the CS deparment list the cid and the number of students enrolled in that course. CSC 370 PAGE 10

11 5. Interpreting SQL queries Based on the instances of page 2, what is the answer to the following queries? For attributes with a NULL value, leave their place empty (as it was done in page 2. (a) [3] SELECT count(*) as count1, count(grade) as count2 FROM Students NATURAL FULL OUTER JOIN Enrolled (b) [3] SELECT cid, count(*) as total FROM Courses NATURAL JOIN Enrolled GROUP BY cid CSC 370 PAGE 11

12 End of examination Total pages: 13 Total marks: 50 CSC 370 PAGE 12