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INTRODUCTION
TO
DATABASE SYSTEM
TOPICS TO BE DISCUSSED……………

Meaning of Database

Characteristics of Database

Database System

Advantages of Database System

Disadvantages of Database System
DATABASE

Database is a collection of related information stored so that it available to
many users for different purposes. The content of database is obtained by
combining data from all the different sources in an organization. So that
data are available to all users and redundant data can be eliminated

A database is well organized collection of data that are related in a
meaningful way which can be accessed in different logical orders but are
stored only once.
CHARACTERISTICS OF DATABASE

Database represents some aspects of real world application. Any change in
real world are reflected in database.

A database is designed and built with data for specific purposes.

It has intended group of users and applications in which these users rae
interested.

Operations like update, insert, retrieve etc. on the database can be carried out in
simple and flexible way.

A database provides logical relationship between its records and data. Thus
various records can be accessed depending on some logical conditions by a single
query from the database
DATABASE SYSTEM
A database system consist of a collection of interrelated data and a set of
programs to access the data. Hence database system is the DBMS software
together with the data itself. It is a software that assist in maintaining and
utilizing a database.
A Database Management System consist of :
A collection of interrelated data. This part of DBMS is usually referred
to as the database
A set of application programs used to access, update manage that data. This
portion forms Data Management System.
The purpose or goal of database system is to provide an environment that is
both convenient and efficient to use in :
Retrieving information from database and
Storing information into database
In other words, a DBMS allows you to store, update and retrieve data hence
making it easy to maintain and retrieve information from a database.
The following figure shows simplified database system environment:
USERS
DATABASE
SYSTEM
DBMS
Software
Queries
Software to process Queries
Software to Access Stored Data
Stored Database
Definitions
Stored Database

The database system contains not only the database itself but also a
complete definition or description of the database structure and constraints.
This definition is stored in system catalog. The information stored in
catalog is called d metadata i.e. data about data.

An important property of database system is that the structure of data files
is stored in the DBMS catalog separately from the access programs. This is
known as program-data independence. Due to this property, we can change
the structure of data files in the catalog but no need to change the
programs.
ADVANTAGES OF DATABASE SYSTEM
Database approach came into existence due to the bottlenecks of file
processing system. In the database approach, the data is stored at a central
location and is shared among multiple users. Thus, the main advantage of
DBMS is centralized data management. The centralized nature of
database system provides several advantages, which overcome the
limitations of the conventional file processing system. These advantages
are listed here.
Controlled data redundancy: During database design, various files are
integrated and each logical data item is stored at central location. This
eliminates replicating the data item in different files, and ensures
consistency and saves the storage space. Note that the redundancy in the
database systems cannot be eliminated completely as there could be some
performance and technical reasons for having some amount of redundancy.
However, the DBMS should be capable of controlling this redundancy in
order to avoid data inconsistencies.
Enforcing data integrity: In database approach, enforcing data integrity is
much easier. Various integrity constraints are identified by database
designer during database design. Some of these data integrity constraints
can be enforced automatically by the DBMS, and others may have to be
checked by the application programs.
Data sharing: The data stored in the database can be shared among
multiple users or application programs. Moreover, new applications can be
developed to use the same stored data. Due to shared data, it is possible to
satisfy the data requirements of the new applications without having to
create any additional data or with minimal modification.
Ease of application development: The application programmer needs to
develop the application programs according to the users’ needs. The other
issues like concurrent access, security, data integrity, etc., are handled by
the DBMS itself. This makes the application development an easier task.
Data security: Since the data is stored centrally, enforcing security
constraints is much easier. The DBMS ensures that the only means of
access to the database is through an authorized channel. Hence, data
security checks can be carried out whenever access is attempted to
sensitive data. To ensure security, a DBMS provides security tools such as
user codes and passwords. Different checks can be established for each
type of access (addition, modification, deletion, etc.) to each piece of
information in the database
Multiple user interfaces: In order to meet the needs of various users
having different technical knowledge, DBMS provides different types of
interfaces such as query languages, application program interfaces, and
graphical user interfaces (GUI) that include forms-style and menu-driven
interfaces. A form-style interface displays a form to each user and user
interacts using these forms. In menu-driven interface, the user interaction is
through lists of options known as menus.
Backup and recovery: The DBMS provides backup and recovery
subsystem that is responsible for recovery from hardware and software
failures. For example, if the failure occurs in between the transaction, the
DBMS recovery subsystem either reverts back the database to the state
which existed prior to the start of the transaction or resumes the transaction
from the point it was interrupted so that its complete effect can be recorded
in the database.
Program-data independence: The independence between the programs
and the data is known as program data independence or data independence
It is an important characteristic of DBMS as it allows changing the
structure of the database without making any changes in the application
programs that are using the database.
Data abstraction: The property of DBMS that allows program-data
independence is known as data abstraction. Data abstraction allows the
database system to provide an abstract view of the data to its users without
giving the physical storage and implementation details.
Supports multiple views of the data: A database can be accessed by many
users and each of them may have a different perspective or view of the
data. A database system provides a facility to define different views of the
data for different users. A views a subset of the database that contains
virtual data derived from the database files but it does not exist in physical
form. That is, no physical file is created for storing the data values of the
view; rather, only the definition of the view is stored.
DISADVANTAGES OF DATABASE SYSTEM
High Cost
Because a complete DBMS is very large and sophisticated piece of software,
it is expensive to purchase.
High Hardware Cost
Additional memory and processing power may be require to run the DBMS.
This results need to upgrade the hardware.
High Programming Cost
Because a DBMS is a complex tool with many features, it requires
experienced programmers which result in extra payment for their hire and
expertise.
Backup and Recovery are more Difficult
This is because of increased complexity and because databases are often
processed by several users concurrently. Determining the exact state of
database at the time of failure may be a problem.
Data Integrity
Since a large number of users could be using a database concurrently
technical safe guards are necessary to ensure that the data remain correct
during operation. The main threat to data integrity comes from several
different users attempting to update same data at the same time.
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