Introduction to Database Management Systems Atul Kahate ALWAYS LEARNING PEARSON

12 Pages·2017·0.96 MB·English

Introduction to
Database Management
Systems
Atul Kahate
ALWAYS LEARNING
PEARSON
Introduction
to
Database
Management Systems
Introduction
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Database
Management Systems
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Atul Kahate
PROJECT MANAGER
/-I/ex Solutions Limited
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Pearson
Education
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To
My Wife Anita
For being the best life partner one could ever hope to find
Daughter Jui
For being so wonderful, lovely, mischievous and cheerful
Son Harsh
For adding some spice to our small but brilliant family
Jorezuord
Like many technologies in the computer industry, the evolution of databases can be tracked back to
research into automating office functions in the 1960s and 1970s. Firms discovered it was becoming
far too expensive to hire people to do certain jobs such as storing and indexing files. They began
investing in research into cheaper and more efficient mechanical solutions.
In 1970, an IBM researcher named Ted Codd published the first article on relational databases. It
outlined an approach that used relational calculus and algebra to allow non-technical users to store
and retrieve large amounts of information. Codd envisaged a system where the user would be able to
access information stored in tables with "natural language" commands.
The article's significance was not recognised because it was far too technical and relied heavily
on mathematics. However, it did lead to IBM starting a research group known as "System R".
Eventually, System R evolved into SQL/DS which later became DB2. The language created by the
System R group, SQL (Structured Query Language) has become the industry standard for relational
databases and is now an ISO standard.
The first database systems built upon the SQL standard appeared at the beginning of the 1980s
from Oracle with Oracle Version 2, and later SQL/DS from IBM, as well as a host of other systems
from other companies.
Relational database technology was continually refined during the 1980s. This was due to feedback
from customers, the development of systems for new industries and the increased use of personal
computers and distributed systems.
By the middle of the 1980s, it had become obvious that there were several fields where relational
databases were not practical due to the types of data they used. These areas included medicine,
multimedia and high energy physics and they needed more flexibility in how their data was
represented and accessed.
This led to research into object oriented databases where users could define their own methods of
access to data and how it was represented and manipulated. This coincided with the introduction of
Object Oriented Programming languages such as C-H- which started to appear in industry at the same
time. Since then, in the late 1990s and the early years of this decade, we have seen huge advances
in the technology behind running databases and securing them.
Since their arrival, databases have expanded in size from the 8MB of data that System R had
been tested with to terabytes of data used for mailing lists, credit card information for banks and so
on. With each increase in the amount of storage available, we have seen a corresponding increase in
the size and complexity of database systems in operation.
In today's scenario, databases are ubiquitous in all modern corporations, so much so, that
professionals carry smaller databases on palmtops or mobile phones. It will be hard to find any
successful organisation that does not deploy databases for their key operations. This subject is now
viii Foreword
being taught and discussed in primary schools in urban areas. This area of technology has spun off
a huge cottage industry around it, spanning from the technical support novice to highly specialised
very large database management gurus.
It is in light of this background that Atul's book is very significant. Effective database management
has become a critical success factor in corporate IT strategy. Although, there are a number of books
on this subject available in the market today, Introduction to Database Management Systems stands
out because of the wide range of topics that it covers and the simple and lucid manner in which it
explains them. It will be of tremendous value to students of this subject, who can also use it as a
reference tool.
While working with Atul over the years, I have always been impressed with his thorough under-
standing of database management and other related topics. He also has outstanding ability to present
his thoughts in the most palatable fashion. I am delighted that he has come out with this book that
explains the theory behind database systems, their architectures and issues in a way that even a
layman can understand. Atul has put to good use his practical experience while working with us at
i-flex, mixed with his very good grasp of theory of databases.
I wish him all the best in his future endeavours.
Deepak Ghaisas
CEO (India Operations)
i-flex Solutions Limited
Pune
(Preface
The traditional mechanism for storing computer data was data files. Data files have been immensely
popular since the 1960s. The earlier commercially successful programming languages such as COBOL
had extensive features related to file processing. In fact, even today, many major computer
applications run on file-based computer systems.
However, all this has also changed in the last few decades. Database Management Systems
(DBMS) has become a subject of great significance in the Information Technology industry. Most
serious business applications need the presence of DBMS in some form or the other. DBMS is
replacing files as the de facto standard for storing data that is medium/long term in nature. This is
especially true in the case of most newly developed applications.
DBMS is a fascinating subject. Many people confuse it with Structured Query Language (SQL).
However, SQL is just one aspect of DBMS technology. Understanding how DBMS technology really
works involves the study of many theoretical concepts, such as database design, modelling, transaction
management, security, concurrency, and so on.
I have read a number of books on DBMS. Most of them explain DBMS technology quite well,
but there is one aspect that I find quite intimidating, and that is the complexity of these books. I
have a strong and sincere belief that without using almost any jargon and mathematics, we can study
most aspects of the DBMS technology. It is intimidating to see complex mathematics and cryptic
symbols one page after the other when learning DBMS. That is the sole reason why I have
attempted to keep the material as simple as it can get. The idea is that even a person with very
little background in computers will be able to grasp the main concepts in DBMS, and if he/she is
interested, can go ahead and study the more complex features.
Here are the main features of the book.
■ Orientation: An attempt has been made to cover the topics in an appropriate sequence, so that
it is sufficient for the managers/professionals/teachers/students to refer to this book alone for
learning about DBMS.
■ Contents'. The book covers all the major concepts in the DBMS technology that a reader at
any level needs to understand.
■ Style: An attempt has been made to keep the language very simple and to make the
explanations extremely lucid.
■ Visual approach: The book features a number of illustrations and diagrams (close to 400) to
enable an easier grasp of the subject.
■ Pedagogical features: Every chapter contains a list of Key Terms and Concepts, Chapter
Summary and self-study questions in the form of True/False questions, Multiple-choice
questions and Detailed questions. In addition, Exercises are also provided at the end of every
chapter.
The chapter-wise organisation of the book is as follows.
Chapter 1 provides a lot of background material to the subject of DBMS. This chapter covers the