DBMS-UNIT 1

Introduction
Database
• By data, it means known facts that can be
recorded and that have implicit meaning.
• A database is a collection of related data .
• For example, consider the names, telephone
numbers, and addresses of the people you know.
You may have recorded this data in an indexed
address book, or you may have stored it on a
diskette, using a personal computer and software
such as DBASE IV or V, Microsoft ACCESS, or
EXCEL.
• This is a collection of related data with an implicit
meaning and hence is a database.
Database management
system
• A database management system (DBMS) is a collection
of programs that enables users to create and maintain a
database. The DBMS is hence a general-purpose
software system that facilitates the processes of
defining, constructing, and manipulating databases for
various applications. Defining a database involves
specifying the data types, structures, and constraints for
the data to be stored in the database. Constructing the
database is the process of storing the data itself on some
storage medium that is controlled by the DBMS.
Manipulating a database includes such functions as
querying the database to retrieve specific data, updating
the database to reflect changes in the miniworld, and
generating reports from the data.
DBMS allows users the
following tasks:
• Data Definition: It is used for creation, modification, and
removal of definition that defines the organization of data
in the database.
• Data Updation: It is used for the insertion, modification,
and deletion of the actual data in the database.
• Data Retrieval: It is used to retrieve the data from the
database which can be used by applications for various
purposes.
• User Administration: It is used for registering and
monitoring users, maintain data integrity, enforcing data
security, dealing with concurrency control, monitoring
performance and recovering information corrupted by
unexpected failure.
Database Systems versus File
Systems
• One way to keep the information on a computer
is to store it in operating system files.
• To allow users to manipulate the information,
the system has a number of application
programs that manipulate the files.
• Keeping organizational information in a file-
processing system has a number of major
disadvantages like Data redundancy and
inconsistency, Difficulty in accessing data,
Atomicity problems, Security problems etc
Need of DBMS
• DBMS is useful in the following ways:
• 1. Ease of Accessing Data
In the file system, different files are created for each user
containing which data they can access. Also, in the file system,
for the user to extract data, there is a need for code or
application. DBMS removes redundancy by granting access to
users and decides which and how many parts of data is
accessible to them from the database. Users can get easy
access to data and can also specify the type of data they want
to extract.
• 2. Storage and Management of Data
• Data cannot be stored in the form of objects in the file
system. The data in the practical world is generally stored in
the form of objects and not files. So, an application is
required to map the data into objects for further usage. In
Need of DBMS
3. Easy and Efficient File Management
In the file system, the entire database runs for every query
operation as files are indexed. It takes a lot of time compared
to DBMS, where objects are indexed based on the attribute
of data. The complex management of memory becomes easy
to handle. With this, retrieval of data is faster than the
traditional file system.
4. Avoiding duplicates and Redundancy
Data normalization is used in DBMS to avoid duplicate data.
5. Concurrent Data Accessing
Users can access data simultaneously through different
applications. In the file system, this simultaneous access
leads to inconsistency. DBMS uses the ACID approach to
tackle the issue.
 Advantages of DBMS
• Controls database redundancy: It can control data
redundancy because it stores all the data in one single
database file and that recorded data is placed in the
database.
• Data sharing: In DBMS, the authorized users of an
organization can share the data among multiple users.
• Easily Maintenance: It can be easily maintainable due to the
centralized nature of the database system.
• Reduce time: It reduces development time and maintenance
need.
• Backup: It provides backup and recovery subsystems which
create automatic backup of data from hardware and software
failures and restores the data if required.
• multiple user interface: It provides different types of user
interfaces like graphical user interfaces, application program
interfaces etc
 Database System Applications
• Banking: For customer information, accounts, and
loans, and banking transactions.
• Airlines: For reservations and schedule information.
Airlines were among the first to use databases in a
geographically distributed manner—terminals situated
around the world accessed the central database system
through phone lines and other data networks.
• Universities: For student information, course
registrations, and grades.
• Telecommunication: For keeping records of calls made,
generating monthly bills, maintaining balances on
prepaid calling cards, and storing information about the
communication networks.
Database System Applications
cntd..
• Finance: For storing information about holdings, sales,
and purchases of financial instruments such as stocks
and bonds.
• Sales: For customer, product, and purchase
information.
• Manufacturing: For management of supply chain and
for tracking production of items in factories,
inventories of items in warehouses/stores, and orders
for items.
• Human resources: For information about employees,
salaries, payroll taxes and benefits, and for generation
of paychecks
Data Abstraction
• For the system to be usable, it must retrieve data
efficiently. The need for efficiency has led
designers to use complex data structures to
represent data in the database.
• Since many database-systems users are not
computer trained, developers hide the complexity
from users through several levels of abstraction, to
simplify users’ interactions with the system;
• Physical level
• Logical Level
• View Level
• Physical level. The lowest level of abstraction
describes how the data are actually stored. The
physical level describes complex low-level data
structures in detail.
• Logical level. The next-higher level of abstraction
describes what data are stored in the database, and
what relationships exist among those data.
• Database administrators, who must decide what
information to keep in the database, use the logical
level of abstraction.
• View level. The highest level of abstraction describes
only part of the entire database. The view level of
abstraction exists to simplify users interaction with
the system. The system may provide many views for
the same database.
DBMS Architecture
• Types of DBMS Architecture:
• 1- Tier Architecture
• 2- Tier Architecture
• 3- Tier Architecture
• 1- Tier Architecture:
• In One- Tier Architecture the database is directly
available to the user, the user can directly sit on the
DBMS and use it i.e.; the client, server and the Database
all present on the same machine. For Example- To learn
SQL we setup SQL server and the database on the local
system.
• Sometimes it may be referred as Centralized system with
single user system.
• Two-tier architecture:
The two-tier architecture is similar to a basic client-
server model. The application at the client end directly
communicates with the database at the server-side. APIs like
ODBC, JDBC are used for this interaction. The server side is
responsible for providing query processing and transaction
management functionalities. On the client-side, the user
interfaces and application programs are run. The application
on the client-side establishes a connection with the server-
side in order to communicate with the DBMS.
An advantage of this type is that maintenance and
understanding are easier, compatible with existing systems.
However, this model gives poor performance when there are
a large number of users.
• Three Tier architecture:
In this type, there is another layer between the client and the
server. The client does not directly communicate with the server.
Instead, it interacts with an application server which further
communicates with the database system and then the query
processing and transaction management takes place. This
intermediate layer acts as a medium for the exchange of partially
processed data between server and client. This type of
architecture is used in the case of large web applications.
• Advantages:
Enhanced scalability due to distributed deployment of
application servers. Now, individual connections need not be
made between client and server.
• Data Integrity is maintained. Since there is a middle layer
between client and server, data corruption can be
avoided/removed.
• Security is improved. This type of model prevents direct
interaction of the client with the server thereby reducing access
 Classification of Database
Management Systems
• Several criteria can be used to classify DBMS.

• Classification Based on Data Model Relational data model

Object Oriented data model

• Classification Based on User Numbers Single user system

• Multi User system

• Classification Based on Database Distribution

• Centralized Distributed Homogeneous

Multi User system

Distributed System