The American University in Cairo
Computer Science Department
CSCI 453
Dr. KHALIL
EXAM - I
Last Name : ...........................................................
Spring 2005
ID: ...................................
First Name: ...........................................................
Solve only 4 questions
Do not turn this page until asked to do so.
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Exam time is 50 minutes.
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Put the answers on the same question sheet, do not use any additional papers, even for scratch.
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Write your name, ID, section no. in the indicated places.
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Read the exam instructions.
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Read the honesty policy.
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Sign the following statement.
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of these actions or her/his answers indicates that she/he did any of them, will receive a punishment
ranging from zero in this exam to failing the course. If repeated, it may lead to dismissal from
AUC.
I have read the honesty policy and exam instructions and I am presenting this
exam as entirely my effort.
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Question
Points
25
25
25
25
Total
100
1
Grade
QUESTION 1 ( 25 points)
Some of the following statements are completely correct while others are partially correct (only part of it that is
incorrect). Mark those statements that are correct and try to correct those that are partially correct.
1. In distributed databases, there is a serious problem with distributed recovery which is the distributed commit.
When a transaction is updating data at several sites, it cannot commit until it is sure that the effect of the
transaction on every site cannot be lost. This means that every site must first have recorded the local effects of the
transactions permanently in the local site log on disk. The Basic 2PL commit protocol is often used to ensure the
correctness of distributed commit.
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2.
The ACID properties of a transaction are Atomicity, Correctioness, Isolation, and Durability.
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3.
Heuristic query optimization depends on the semantics and not the syntax of the database. It is based only on the
general qualities of the relational algebra expressions and involves substituting relational algebra expressions with
more efficient expressions using equivalence preserving transformation rules.
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4.
Web database gateways link stateless systems (i.e., databases) with a stateful, connectionless protocol (i.e., HTTP).
In other words, a Web database gateway (middleware)is a bridge between the Web and a DBMS, and its objective
is to provide a Web-based application the ability to manipulate data stored in the database.
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5.
The basic 2PL protocol requires every transaction lock all the items it needs in advance; if any of the items cannot be
obtained, none of the items are locked. This solution obviously limits concurrency.
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6.
In distributed database environment, copy transparency means that the system supports the optional existence of
multiple copies of database objects while location transparency means that a user can submit a query that accesses
distributed objects without having to know where objects are.
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7. Replication is useful in improving the query processing and optimization.
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8.
In general, a fragment of relation R can be specified by a SELECT-PROJECT
L(C(R)).
If C = True and L <> ATTRS(R), we get a mixed fragment
If C <> True and L = ATTRS(R), we get a vertical fragment.
If C <> True and L <> ATTRS(R), we get a horizontal fragment.
A relation can itself be considered a fragment with C=True and L= ATTRS(R).
combination of operations
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9.
For large databases, the communication cost is the one considered in the systematic optimization of query processing,
while for distributed databases, the main emphasis is on the computation cost.
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10. In distributed databases with No Local Autonomy, direct access by local transactions to a server is permitted. Such
type of DDBMS is called fragmented DDBMS (or a multidatabase system). In such a system, each server is an
independent and autonomous centralized DBMS that has its own local users. Each server can authorize access to
particular portions of its database by specifying an export schema, which specifies the part of the database that may
be accessed by a certain class of nonlocal users.
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QUESTION 2 ( 25 points)
Consider the following relational schema for a bank.
BRANCH (BranchName, Location, Manager)
CUSTOMER (AccountNo, CustomerName, BranchName, Balance)
TRANSACTION (TransactionNo, AccountNo, Tdate, Ttype, Tvalue)
The bank consists of one main branch and several other branches. There is a computer site for each branch. In the site of
the main branch, it is required to maintain the data of all customers (and their transactions) of that branch besides data
about all customers (and their transactions) of all other branches having a balance that exceeds LE 1,000,000. In the
computer site of each other branch, it is required to maintain all information about only the customers and transactions
of that branch.
a)
Design a distributed database over the different sites according to the given requirements (write a SQL query
that will produce each required fragment in each computer site). You can refer to the main branch as “Main”
and to any other branch as “BranchX”.
b) Determine the type and replication level of each resulting fragment.
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QUESTION 3 ( 25 points)
a) In Web applications, there are two main general approaches for the server-side solutions: the CGI (Common
Gateway Interface) and the APIs (Application Programming Interface). An API or CGI works as a Web server
interface to the web-to-database middleware. Name on the following scheme the different entities and
interfaces of a typical web system.
b) Give the technical comparison between the CGI approach and the API approach regarding the given technical
issues:
Features
CGI
Language-independent
Runs in different process from
core Web server
Open standard
Web server architectureindependent
Supports distributed computing
Multiple, extensible roles
Memory sharing with other
processes
Does NOT create new process
for each instance
Easy to use
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APIs
QUESTION 4 ( 25 points)
. Consider the given relational database schema for a university application. The primary key of each relation is underlined.
STUDENT (StudentNumber, Name, Class)
DEPARTMENT (DeptCode, DeptName)
MAJOR (StudentNumber, MajorDeptCode)
MINOR (StudentNumber, MinorDeptCode)
INSTRUCTOR (InstNum, Name, Status, DeptCode)
COURSE (DeptCode, CourseNumber, CourseName, CreditHours)
PREREQUISITE (DeptCode, CourseNumber, PreDeptCode, PreCourseNumber)
SECTION (DeptCode, CourseNumber, SectionIdentifier, Semester, Year, InstNum)
TRANSCRIPT(StudentNumber, DeptCode, CourseNumber, SectionIdentifier, Semester, Year,
Grade)
Put the following queries in more efficient expressions:
1.
(((((STUDENT join MAJOR) join DEPARTMENT) W here CLASS=”Junior”)[Name, DeptName]) W here
DeptName=”Computer Science”)
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2.
((STUDENT join TRANSCRIPT) W here DeptCode=”CSCI”)[StudentNumber, Name]
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3.
((((((STUDENT join TRANSCRIPT) W here DeptCode=”CSCI”) W here CourseNumber=453) W here
Semester=”Spring”) W here Year=2004)[StudentNumber, Name, SectionIdentifier, Grade])[Name, Grade]
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4.
(STUDENT join MAJOR) [StudentNumber]
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QUESTION 5 ( 25 points)
A DBMS attempts run the following schedule:
T1
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T2
Read_lock(Y)
Read_item(Y)
Y := Y * 2
Write_lock(Y)
Write_item(Y)
Read_lock(X)
Read_item(X)
X=X+Y
Read_lock(Y)
Read_item(Y)
Read_lock(X)
Read_item(X)
X=X+Y
Write_lock(X)
Write_item(X)
Unlock(X)
Unlock(Y)
Write_lock(X)
Write_item(X)
Unlock(X)
Unlock(Y)
N.B. It would be useful and saving time to refer to line numbers to clarify your answer.
1. Draw a wait-for-graph. How can you tell that deadlock has occurred?
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2. Write down the wait-die protocol and redo the same schedule using the wait-die scheme.
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3. Write down the wound-wait protocol and redo the same schedule using the wound-wait
scheme.
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QUESTION 6 ( 25 points)
a. A schedule S is said to be conflict serializable if it is conflict equivalent to some serial schedule S’. Check the
serializability of the following schedule. If the schedule is serializable, determine its equivalent serial schedule.
Sc: r3(Z); r3(Y); w3(Y); r1(Y); r1(Z); r2(X); w2(X); w1(Y);w1(Z); r3(X);
r2(Y);w2(Y);w3(x);
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b. A DBMS is a complex software system. The following diagram shows a simplified structure of a typical DBMS.
Name on the diagram every component, interface, and users involved in such system.
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