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lOMoARcPSD|18938463DBMS Final - complete course note
database management system (Pokhara University)
Studocu is not sponsored or endorsed by any college or university
Downloaded by Sanjiv Tamang (tamangsanjiv2015@gmail.com)
, lOMoARcPSD|18938463
Downloaded from: http://www.bsccsit.com/
Chapter 1
Chapter-1
Data:
Data are the raw facts that can be obtained after some experiments or observations. Raw data
is of no use until and unless we process it to find some useful information form it.
Database:
A database is the collection of related persistent data and contains information relevant to an
enterprise. The database is also called the repository or container for a collection of data files.
For example, university database for maintaining information about students, courses and
grades in university
Database Management System:
Management of data involves a way to store data and also provides a mechanism for
manipulation of that data. Database management systems are basically designed to manage large
volume of information.
A database system is basically just a computerized record-keeping system. A database
system involves four major components: data, hardware, software, and users. The database
management system (DBMS) is the software that handles all access to the database. It is
defined as the collection of interrelated data and a set of programs to access those data.
The primary goal of DBMS is to store and retrieve data in both convenient (easy method)
and efficient (capable of performing well) manner. Some of the examples of DBMS are Oracle,
SQL-Server, MySQL, MS Access etc.
Applications of DBMS:
• Banking:
To store information about customers, their account number, balance etc.
• Airlines:
For reservations and schedule information.
• Telecommunication:
To keep records of customers, call made, balance left, generating monthly bills
etc.
• Universities:
To keep records of students, courses, marks of students etc.
• Sales:
To keep information of customers, products list, purchase information etc.
• Manufacturing:
To store orders, tracking production of items etc.
• Human Resources:
To keep records of employee, their salary, bonus etc.
Prepared by: Er. Bipul Kr. Yadav
Downloaded by Sanjiv Tamang (tamangsanjiv2015@gmail.com)
, lOMoARcPSD|18938463
Downloaded from: http://www.bsccsit.com/
Chapter 1
Characteristics of database approach:
The main characteristics of database approach are discussed below:
1. Self describing nature of database system:
The fundamental characteristic of the database approach is that the database
system contains not only the database itself but also complete definition or description of
the database structure. This definition is stored in the DBMS catalog which contains the
information such as the structure of each file, the type and storage format of each data
item. Eg.
2. Insulation between programs and data :
In traditional file processing system, the structure of data file is embedded in the
application program. Hence if we have to make any changes in the format of the data, the
whole application program will also have to be changed.
But in the case of DBMS, database and the application program are separately
situated. The structure of data files is stored in the DBMS catalog separately from the
access programs. Hence in most cases DBMS access programs do not need such changes.
We call this property as program-data independence.
For example, a file access program may be written in such a way that it can just
access the name of a customer of any company but if we want to add another field, say,
address of the customer, then in such a case this program will no longer be useful. But in
the case of the DBMS, we just have to add the new field “address” in the catalog and the
next time DBMS refers to the catalog, the new structure of the records will be accessed
and hence we do not have to make change in the program.
3. Support of multiple view of the data:
Let us consider an example of student information system of a college, where all
the data of student, courses, information of college etc are stored in a database. It is
Prepared by: Er. Bipul Kr. Yadav
Downloaded by Sanjiv Tamang (tamangsanjiv2015@gmail.com)
, lOMoARcPSD|18938463
Downloaded from: http://www.bsccsit.com/
Chapter 1
obvious that there is more than one user of this system and also their interest is different.
i.e. student are generally interested in finding out the marks obtained, whereas teachers
are able to put marks, view information about students, similarly, visitors are able to find
the information of the college.
A database typically has many users, and their perspective of viewing the database is
different. In the example given above, every user is accessing data from the same
database but what they see and can access is different. A view may be subset of the
database or it may contain virtual data that is derived from the database files but is not
stored explicitly.
4. Sharing of data and multi user transaction processing:
Database system should allow multiple users to access same database at the same
time. For example, in online air ticket reservation system many users are accessing the
same site at the same time. Hence for every seat, DBMS should ensure that only one user
should be given access to reserve the seat.
Hence to ensure the correctness of this type of transaction DBMS must include
concurrency control software to ensure that several users trying to update same data do so
in a controlled manner so that the result of the updates is correct. In order to do so,
DBMS uses lock based protocol and time stamp based protocol.
Purpose of Database System:
Traditionally, file processing system was used to manage information. It stores data in
various files of different application programs to extract or insert data to appropriate file. File
processing system has several drawbacks due to which database management system is required.
Database management system removes problems found in file processing system. Some of the
major problems of file processing systems are:
1. Data redundancy and inconsistency:
In file processing system, different programmer creates files and writes
application programs to access it. After a long period of time files may exist with
different formats and application programs may be written in many different
programming languages. Moreover, same information may be duplicated in several files.
We have to pay for higher storage and access cost for such redundancy. It may leads
database in inconsistent state because update made may be reflected in one file but it may
not be reflected in another files where same information exist in another files.
2. Difficulty in accessing data:
In file processing system, we can not easily access required data stored in
particular file.
For each new task we have to write a new application program. File processing
system can not allow data to be retrieve in convenient and efficient manner.
3. Integrity problem:
In database, we required to enforce certain type consistency constraints to ensure
the database correctness or to enforce certain business rules. It is in fact called integrity
constraints (e.g. account balance > 0), integrity of database need not to be violated. In file
processing system, integrity constraint becomes the part of application program.
Prepared by: Er. Bipul Kr. Yadav
Downloaded by Sanjiv Tamang (tamangsanjiv2015@gmail.com)
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