TEST 1
CSCE 520 – Spring 2011
Name:
Major:
SSN (last 4 digits):
Q1 (30)
Q2 (20)
Q3 (15)
Q4 (15)
Q5 (20)
Bonus (5)
Q6 (20) – Grad. only
Total
Answer the following questions. Be brief and precise. You
have 1 hour 15 minutes to finish the test. Undergraduate students must answer questions 1,…,
5; graduate students must answer additional question 6 for full credit. The bonus question is
open for everyone.
1.
You are asked to design a database system for a health club. The database would
contain data about customers, their training, contact numbers, etc. Show the main steps
you would perform for designing and implementing the database. (Don’t show the actual
schemas!)
Multiple good answers may exist. Justify your reasoning.
2.
Consider the relation schema:
Ship(class, type, country, numGuns, bore, displacement)
Write the relational algebra expression to ensure that no class of ships may have guns with larger
than 16-inch bore.
bore>16 (Ship) = 
How can you enforce the same constraints using SQL?
During CREATE TABLE statement:
CREATE TABLE Ship (
…
Bore INT
CHECK (Bore <=16)
);
3.
Describe the characteristics of relations that make them different from ordinary tables and files.
Multiple characteristics exist, such as:
 Structure
 Granularity and efficiency of data access
 Semantics of stored data
 Support for consistency and persistent storage
 Support for concurrency
 Etc.
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4.
Describe the difference between natural join and theta-join when the condition of the theta join is
to equate the attributes appearing in the schemas of both relations. Describe the schema, number
of tuples, and control of join operation.
Schema
Number of
Tuples
Control of
join
Natural join
All attributes of the relations
With single occurrence of the
Overlapping attributes
Theta-join
All attributes of the relations
with multiple occurrence of the
overlapping attributes
Joins only those tuples that have
the same values for overlapping
Attributes
Automatically for shared attributes
joins all tuples and chooses those
that satisfy the selection cond.
Cartasian product
5.
Why is it important to have ACID properties of transactions?
Without ACID properties, we cannot guarantee transaction correctness.
Show an example, when the violation of one or more of the ACID properties would create an
incorrect transaction execution.
Multiple examples exist, for example, only ½ of a transaction is executed, or incorrect execution,
e.g., allow for bank account to have negative balance, etc.
6.
What is the difference between the SELECT operator () in relational algebra and the SELECT
keyword in SQL?
Both projects the selected attributes. The main difference is the  works on sets, and the output is
a set, while SQL SELECT is a bag. That is if the answer has more than one occurrences of the
same tuple,  will return only one of them, while SQL SELECT will return all. We can eliminate
the duplicates of the SQL SELECT by using the “SELECT DISTINCT” command.
Assume that R(A,B) and S(B,C) are relations. Convert the following relational algebra
expression to a corresponding SQL statement: AB (C=3(R |X| S) (|X| is the natural join)
SELECT A, R.B
FROM R, S
WHERE R.B = S.B AND C= 3 ;
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