ComPUTeR ScIence
TEXTBOOK FOR CLASS XII
2024-
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12130 – COMPUTER SCIENCE
Textbook for Class XII ISBN 978-93-5292-338-0
First Edition
September 2020 Bhadrapada 1942 ALL RIGHTS RESERVED
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Meetu Sharma, DTP Operator, DESM
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FOReWORD
Computer science as a discipline has evolved over the years and has
emerged as a driving force of our socio-economic activities. It has made
continuous inroads into diverse areas — be it business, commerce, science,
technology, sports, health, transportation or education. With the advent
of computer and communication technologies, there has been a paradigm
shift in teaching-learning at the school level. The role and relevance of this
discipline is in focus because the expectations from the school pass-outs
have grown to be able to meet the challenges of the 21st century. Today, we
are living in an interconnected world where computer-based applications
influence the way we learn, communicate, commute or even socialise!
There is a demand for software engineers in various fields like
manufacturing, services, etc. Today, there are a large number of
successful startups delivering different services through software
applications. All these have resulted in generating interest for this subject
among students as well as parents.
Development of logical thinking, reasoning and problem-solving skills
are fundamental building blocks for knowledge acquisition at the higher
level. Computer plays a key role in problem solving with focus on logical
representation or reasoning and analysis.
This textbook focuses on the fundamental concepts and
problem-solving skills while opening a window to the emerging and
advanced areas of computer science. The newly developed syllabus
has dealt with the dual challenge of reducing curricular load as well as
introducing this ever evolving discipline. This textbook also provides space
to Computational Thinking and Artificial Intelligence, which envisaged in
National Education Policy, 2020.
As an organisation committed to systemic reforms and continuous
improvement in the quality of its products, NCERT welcomes comments and
suggestions which will enable us to revise the content of the textbook.
HRUSHIKESH SENAPATY
Director
New Delhi National Council of Educational
August 2020 Research and Training
2024-
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PRefACe
In the present education system of our country, specialised or discipline
based courses are introduced at the higher secondary stage. This stage
is crucial as well as challenging because of the transition from general
to discipline-based curriculum. The syllabus at this stage needs to have
sufficient rigour and depth while remaining mindful of the comprehension
level of the learners. Further, the textbook should not be heavily loaded
with content.
Computers have permeated in every facet of life. Study of basic concepts
of computer science has been desirable in education. There are courses
offered in the name of Computer Science, Information and
Communication Technology (ICT), Information Technology (IT), etc., by
various boards and schools up to secondary stage, as optional. These
mainly focus on using computer for word processing, presentation tools
and application software.
Computer Science (CS) at the higher secondary stage of school education
is also offered as an optional subject. At this stage, students usually opt
for CS with an aim of pursuing a career in software development or related
areas, after going through professional courses at higher levels. Therefore,
at higher secondary stage, the curriculum of CS introduces basics of
computing and sufficient conceptual background of Computer Science.
The primary focus is on fostering the development of computational
thinking and problem-solving skills. This book has 13 chapters covering
the following broader themes:
• Data Structure: understanding of important data structure Stack,
Queue; Searching and Sorting techniques.
• Database: basic understanding of data, database concepts, and
relational database management system using MySQL. Structured
query language — data definition, data manipulation and data
querying.
• Programming: handling errors and exceptions in programs written
in Python; handling files and performing file operations in Python.
• Network and Communication: fundamentals of Computers
networks, devices, topologies, Internet, Web and IoT, DNS. Basics
of Data communication — transmission channel, media; basics of
protocols, mobile communication generations.
• Security Aspects: introduction to basic concepts related to network
and Internet security, threats and prevention.
Each chapter has two additional components — (i) activities and (ii)
think and reflect for self assessment while learning as well as to generate
further interest in the learner. A number of hands-on examples are given to
gradually explain methodology to solve different types of problems across
the Chapters. The programming examples as well as the exercises in the
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chapters are required to be solved in a computer and verify with the given
outputs.
Box items are pinned inside the chapters either to explain related
concepts or to describe additional information related to the topic covered
in that section. However, these box-items are not to be assessed through
examinations.
Project Based Learning given as the end includes exemplar projects
related to real-world problems. Teachers are supposed to assign these or
similar projects to be developed in groups. Working in such projects may
promote peer-learning, team spirit and responsiveness.
The chapters have been written by involving practicing teachers
as well as subject experts. Several iterations have resulted into this
book. Thanks are due to the authors and reviewers for their valuable
contribution. I would like to place on record appreciation for Professor
Om Vikas for leading the review activities of the book as well as for his
guidance and motivation to the development team throughout. Comments
and suggestions are welcome.
New Delhi Rejaul Karim Barbhuiya
20 August 2020 Assistant Professor
Central Institute of
Educational Technology
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TexTBOOk DevelOPMenT COMMITTee
CHIEF ADVISOR
Om Vikas, Professor (Retd.), Former Director, ABV-IIITM, Gwalior, M.P.
MEMBERS
Anju Gupta, Freelance Educationist, Delhi
Anuradha Khattar, Assistant Professor, Miranda House, University of Delhi
Chetna Khanna, Freelance Educationist, Delhi
Faheem Masoodi, Assistant Professor, Department of Computer Science,
University of Kashmir
Harita Ahuja, Assistant Professor, Acharya Narendra Dev College, University
of Delhi
Mohini Arora, HOD, Computer Science, Air Force Golden Jubilee Institute,
Subroto Park, Delhi
Mudasir Wani, Assistant Professor, Govt. College for Women Nawakadal,
Sri Nagar, Jammu and Kashmir
Naeem Ahmad, Assistant Professor, Madanapalle Institute of Technology
and Science, Madanapalle, Andhra Pradesh
Purvi Kumar, Co-ordinator, Computer Science Department, Ganga
International School, Rohtak Road, Delhi
Priti Rai Jain, Assistant Professor, Miranda House, University of Delhi
Sangita Chadha, HOD, Computer Science, Ambience Public School,
Safdarjung Enclave, Delhi
Sharanjit Kaur, Associate Professor, Acharya Narendra Dev College,
University of Delhi
MEMBER-COORDINATOR
Rejaul Karim Barbhuiya, Assistant Professor, CIET, NCERT, Delhi
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AcknOWLeDGemenTs
The National Council of Educational Research and Training
acknowledges the valuable contributions of the individuals and
organisations involved in the development of Computer Science textbook
for Class XII.
The Council expresses its gratitude to the syllabus development team
including MPS Bhatia, Professor, Netaji Subhas Institute of Technology,
Delhi;
T. V. Vijay Kumar, Professor, School of Computer and Systems Sciences,
Jawaharlal Nehru University, New Delhi; Zahid Raza, Associate Professor,
School of Computer and Systems Sciences, Jawaharlal Nehru University,
New Delhi; Vipul Shah, Principal Scientist, Tata Consultancy Services,
and the CSpathshala team; Aasim Zafar, Associate Professor, Department
of Computer Science, Aligarh Muslim University, Aligarh; Faisal Anwer,
Assistant Professor, Department of Computer Science, Aligarh Muslim
University, Aligarh; Smruti Ranjan Sarangi, Associate Professor,
Department of Computer Science and Engineering, Indian Institute of
Technology, Delhi; Vikram Goyal, Associate Professor, Indraprastha
Institute of Information Technology (IIIT), Delhi; and Mamur Ali, Assistant
Professor, Department of Teacher Training and Non-formal Education
(IASE), Faculty of Education, Jamia Millia Islamia, New Delhi.
The Council is thankful to the following resource persons for
providing valuable inputs in developing this book — Veer Sain Dixit,
Assistant Professor, Atma Ram Sanatan Dharma College, University of
Delhi; Mukesh Kumar, DPS RK Puram, Delhi; Aswin K. Dash, Mother’s
International School, Delhi; Anamika Gupta, Assistant Professor, Shaheed
Sukhdev College of Business Studies, University of Delhi, Sajid Yousuf
Bhat, Assistant Professor, University of Kashmir, Jammu and Kashmir.
The council is grateful to Prof. Sunita Farkya, Head, Department of
Education in Science and Mathematics, NCERT and Prof. Amarendra P.
Behera, Joint Director, CIET, NCERT for their valuable cooperation and
support throughout the development of this book.
The Council also gracefully acknowledges the contributions of Meetu
Sharma, Graphic Designer cum DTP Operator; Kanika Walecha, DTP Operator;
Pooja, Junior Project Fellow; in shaping this book. The contributions of the
office of the APC, DESM and Publication Division, NCERT, New Delhi, in
bringing out this book are also duly acknowledged.
The Council also acknowledges the contribution of Ankeeta Bezboruah
Assistant Editor (Contractual) Publication Division, NCERT for copy editing
this book. The efforts of Naresh Kumar, DTP Operator (Contractual),
Publication Division, NCERT are also acknowledged.
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COnTenTs
FOREWORD iii
PREFACE v
CHAPTER 1 EXCEPTION HANDLING IN PYTHON 1
1.1 Introduction 1
1.2 Syntax Errors 1
1.3 Exceptions 3
1.4 Built-in Exceptions 3
1.5 Raising Exceptions 4
1.6 Handling Exceptions 7
1.7 Finally Clause 13
CHAPTER 2 FILE HANDLING IN PYTHON 19
2.1 Introduction to Files 19
2.2. Types of Files 20
2.3 Opening and Closing a Text File 21
2.4 Writing to a Text File 23
2.5 Reading from a Text File 25
2.6 Setting Offsets in a File 28
2.7 Creating and Traversing a Text File 29
2.8 The Pickle Module 32
CHAPTER 3 STACK 39
3.1 Introduction 39
3.2 Stack 40
3.3 Operations on Stack 42
3.4 Implementation of Stack in Python 43
3.5 Notations for Arithmetic Expressions 46
3.6 Conversion from Infix to Postfix Notation 47
3.7 Evaluation of Postfix Expression 49
CHAPTER 4 QUEUE 53
4.1 Introduction to Queue 53
4.2 Operations on Queue 55
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4.3 Implementation of Queue using Python 56
4.4 Introduction to Deque 59
4.5 Implementation of Deque Using Python 61
CHAPTER 5 SORTING 67
5.1 Introduction 67
5.2 Bubble Sort 68
5.3 Selection Sort 71
5.4 Insertion Sort 74
5.5 Time Complexity of Algorithms 77
CHAPTER 6 SEARCHING 81
6.1 Introduction 81
6.2 Linear Search 82
6.3 Binary Search 85
6.4 Search by Hashing 90
CHAPTER 7 UNDERSTANDING DATA 97
7.1 Introduction to Data 97
7.2 Data Collection 101
7.3 Data Storage 102
7.4 Data Processing 102
7.5 Statistical Techniques for Data Processing 103
CHAPTER 8 DATABASE CONCEPTS 111
8.1 Introduction 111
8.2 File System 112
8.3 Database Management System 115
8.4 Relational Data Model 120
8.5 Keys in a Relational Database 123
CHAPTER 9 STRUCTURED QUERY LANGUAGE (SQL) 131
9.1 Introduction 131
9.2 Structured Query Language (SQL) 131
9.3 Data Types and Constraints in MySQL 133
9.4 SQL for Data Definition 134
9.5 SQL for Data Manipulation 141
9.6 SQL for Data Query 144
9.7 Data Updation and Deletion 154
9.8 Functions in SQL 156
9.9 GROUP BY Clause in SQL 167
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9.10 Operations on Relations 169
9.11 Using Two Relations in a Query 172
CHAPTER 10 COMPUTER NETWORKS 181
10.1 Introduction to Computer Networks 181
10.2 Evolution of Networking 183
10.3 Types of Networks 184
10.4 Network Devices 187
10.5 Networking Topologies 191
10.6 Identifying Nodes in a Networked Communication 194
10.7 Internet, Web and the Internet of Things 195
10.8 Domain Name System 197
CHAPTER 11 DATA COMMUNICATION 203
11.1 Concept of Communication 203
11.2 Components of data Communication 204
11.3 Measuring Capacity of Communication Media 205
11.4 Types of Data Communication 206
11.5 Switching Techniques 208
11.6 Transmission Media 209
11.7 Mobile Telecommunication Technologies 215
11.8 Protocol 216
CHAPTER 12 SECURITY ASPECTS 223
12.1 Threats and Prevention 223
12.2 Malware 224
12.3 Antivirus 230
12.4 Spam 231
12.5 HTTP vs HTTPS 231
12.6 Firewall 232
12.7 Cookies 233
12.8 Hackers and Crackers 234
12.9 Network Security Threats 235
CHAPTER 13 PROJECT BASED LEARNING 241
13.1 Introduction 241
13.2 Approaches for Solving Projects 242
13.3 Teamwork 243
13.4 Project Descriptions 245
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