INTRODUCTION
Database system, plays a vital role in organising data about a particular enterprise. Consider an
example of a company which stores data about following :
Employees ( employee number ,name, address ,salary)
Department( department number, department name ,location )
project (project name, project number, location)
Therefore, a system is needed which can effectively organise the data, organise the data
and also use it to analyse and guide operations of the company.
CONCEPT OF DATABASE MANAGEMENT SYSTEM:
database management system consist two components first database.
1. DATABASE -It’s a collection of data
2. SYSTEM or set of programs which are used to access and manage the database. DBMS
organize the information ,maintain and retrieve it effectively as and when required.
CONCEPT OF DATA:
data are facts or undoubted information used for different computational or calculations. For
example, the facts related to an employee like employee number, name, salary, designation etc.
INFORMATION
Now what is information when these data are retrieved or processed to find answers of questions like
what is employee number of employee whose salary is more than 10,000? THEN IT BECOME
INFORMATION. THUS INFORMATION IS A PROCESSED FORM OF DATA.
FULL DEFINATION OF DBMS
A database, is a collection of interrelated data which represents some aspects of real world. Database has
some inherent meaning and is related to a particular group of users or applications.
For example - database of a college, May contain data about students, faculties, courses etc. which are
related to each other with certain relations like -faculty teaches students, students are enrolled in courses
etc.
The primary objective of a DBMS is to provide an environment that is convenient and efficient to
use ,in retrieving information from and storing information into the database.
DBMS ALLOWS USERS TO THE FOLLOWING TASKS:
1. DATA DEFINITION : It is used for creation, modification, and removal of database objects that
defines the organization of data in the database.
2. DATA UPDATION : It is used for the insertion, modification, and deletion of the actual data in the
database.
3. DATA RETRIEVAL : It is used to retrieve the data from the database which can be used by
applications for various purposes.
4. USER ADMINISTRATION : It is used for registering and monitoring users,maintaining data
integrity, enforcing data security, dealing with concurrency control, monitoring performance and
recovering information corrupted by unexpected failure.
5. For avoiding data redundancy and inconsistency
DATA REDUNDANCY
Some data elements like name, address, identification code are used in various applications. It is
stored in multiple data files. There is a repetition of data files. This is referred to as data
REDUNDANCY.
DATA INCONSISTENCY
For example, consider an employee management system , if address of an Employee which is
stored at two places and is updated at only one place Then the system will give conflicting
information and it becomes inconsistent data.
FILE SYSTEM V/S DBMS
File system stores data in The form of records and data which are files managed by operating
system and uses application program to extract information from the file.
A major advantage the database approach has over the conventional approach is that a
database system provides centralised control of data.
ADVANTAGES OF DBMS :
1.Database redundancy : It controls data redundancy because it stores all the data in one
single database file and that recorded data is placed in the database.
2. Data sharing : In DBMS, the authorized users of an organization can share the data
among multiple users.
3. Easy maintenance : It can be easily maintainable due to the centralized nature of the
database system.
4. Reduce time : It reduces development time and maintenance need.
5. Backup : It provides backup and recovery subsystems which create automatic backup of
data from hardware and software failures and restores the data if required.
6. Multiple user interface : It provides different types of user interfaces like graphical user
interface, application program interface.
DISADVANTAGES OF DBMS :
1. Cost of hardware and software : It requires high speed of data processor and large memory
size to run DBMS software.
2. Size : It occupies a large space of disks and large memory to run efficiently.
3. Complexity : Database system creates additional complexity and requirements.
4. Higher impact of failure : Failure is highly impacted the database because in most of the
organization, all the data stored in a single database and if the database is damaged due to
electric failure or database corruption then the data may be lost forever.
SCHEMA
the overall design of the database is called the database schema.
INSTANCES –
the collection of information stored in the database at a particular moment is called instances.
DATA ABSTRACTION
Data abstraction is one of the fundamental characteristics of any database management system, which
helps in making data more accurate and easy to use. abstraction refers to the act of representing essential
features without including background, details or explanations. So the data abstractions refer to the act of
representing data without giving details that how data are stored or mentioned.
Data abstraction prevents irrelative information at a particular level. Complexity of data is hide
through several levels of abstraction so as to simplify user interaction with the system.
DIFFERENT LEVELS OF DATA ABSTRACTION ARE
1. Physical level or internal level.
It is the lowest level of abstraction which specifies storage detail that how data are actually stored on desk
or on tips. Complex low-level data structures are described in detail at this level. The design of data
structure described and this level is called physical schema.
2. Logical level or conceptual view.
The next higher level of abstraction describes what data are stored in the database and what relationship
exist among those data. There is only one conceptual schema for database. The logical level of abstraction
is used by database administrators, who decide what information is to be kept in the database.
3. View level or external level.
It is the highest level of abstraction which describes different views of the entire database. These views are
designed according to the requirement of user who wants to access only a part of the database. For
example, ERP of this college
