NPTEL Data Base Management System Week 8 Assignment Answers 2025

1. Identify the cost estimation ofa query evaluation plan, if 9000 blocks are required to transferred
from the disk and the required number of disk seeks are 25.

Time to transfer one block: tr = 5 milliseconds.
Time for one seek: ts = 0.4 seconds.

a) 40 Seconds
b) 45 Seconds
c) 50 Seconds
d) 55 Seconds

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3. Let us consider the following statistics for two relations Instructor and Job_Assignments:

Number of records of Instructor: Instructor = 5050.
Number of blocks of Instructor: bInstructor = 30.
Number of records of Job Assignments: AJob_Assignments = 1050.
Number of blocks of Job Assignments: bJob_Assignments = 10.

Let us consider a natural join of Instructor and Job Assignments relations (Instructor A Job _Assignments). Identify the required number of block transfers in the worst case (enough memory only to hold one block of each relation) using Nested-loop join and assume Instructor as the outer relation.

a) 40000 block transfers
b) 40030 block transfer
c) 50030 block transfers
d) 50530 block transfers

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7. Consider the following relational schema:
INSTRUCTOR (InstructerID, Name, HireDate)
COURSE(CourseID, CourseName, Credits)
JOB_ASSIGNMENTS (InstructorID, CourseID, JobTitle, StartDate, EndDate)

Four relational algebra queries are given below:

Q1: ^σStartDate= 2023-01-01 › (INSTRUCTOR X JOB_ASSIGNMENTS)
Q2: ^πStartDate, Name INSTRUCTOR A JOB-ASSIGNMENTS)
Q3: ^πName (INSTRUCTOR A JOB _ASSIGNMENTS)
Q4:^πName (^σ INSTRUCTOR. InstructorID=JOB_ASSICNMENTS. Instructor ID(INSTRUCTOR× JOB_ASSIGNMENTS))

Identify the correct options from the options given below.

a) Q1 is equivalent to Q2.
b) Q1 is not equivalent to Q2.
c) Q3 is equivalent to Q4.
d) Q3 is not equivalent to Q4.