A distributed database consists of multiple, interrelated databases spread across different locations in a network, managed by a distributed database management system (DDBMS) that ensures user access is seamless. DDBMS can be homogeneous (with identical software) or heterogeneous (with different systems), each offering specific advantages like enhanced performance and improved communication, but also posing challenges in management and security. Key features include data fragmentation and replication, which enhance availability and access speed across various locations.

1. Prof. Neeraj Bhargava
Pooja Dixit
Department of Computer Science
School of Engineering & System Science
MDS, University Ajmer, Rajasthan, India
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2.  A distributed database is a collection of multiple, logically
interrelated database distributed over a computer network.
 it is a collection of two or more database that are situated to
other locations on the same network or on entirely different
networks. some part of databases are stored in different
multiple physical location or site and processing is
distributed in different multiple nodes.
 Simply, a distributed database management system is the
software that manages the distributed database and allow to
access them that provide distributed environment and make
it transparent to the users.
 Definition: it is a centalized software system that manages or
control a distributed database in a manner as if it were all
stored in a single location.
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3.  For example: in a banking system bank may implement their
database on a different physical location rather than a single or in
centralized manner. In banking system all computer may located at
local branch office like jaipur, Amritsar. A network enable these
branch office to communicate with each other, and DDBMS allow to
access those data from another branch office.
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4. A DDBMS has the following characteristics:
 They are collection of logically interconnected
data.
 data are divided into smaller fragments.
Fragments can be replicated or allocated to all
connected sites.
 all interconnected sites or nodes are linked
with each other by using Network.
 Data are controlled each and every site by the
DBMS.
 Each Distribute Database Management system
takes part in at least one global application.
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5. 5
Centralized Database Distributed Database
It is a type of database that containes only single database
located on single location in the network
It is type of database that comprises eith two or more
database files located on different location using network
User can access same data or file on single location. It allow multiple user to access and share data
simultaneously
Managing, updating and backup of data are easier but only
on one database file.
It require time synchronization for share, update data on
multiple database file.
If multiple user wants to access same database then It takes
more time for accessing data
It provide faster accessing of data from databases.
In case of any failure in database then user can’t access those
data.
Distributed environment allow to access data anywhere in
case of any fail.
It has more data consistency and also provide the complete
view to the user.
Can have data replications. And there can be some data
inconsistency.

6. A database user can access distributed database through:
 Local application: applications which do not require data from
other sites.
 Global applications: applications which do require data from
other sites.
A DDBMS mainly classified into two types:
 Homogenous Distributed database management systems: has
identical software and hardware running all databases instances,
and may appear through a single interface as if it were a single
database.
 Heterogeneous Distributed database management systems: may
have different hardware, operating systems, database
management systems, and even data models for different
databases.
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7.  In a homogeneous distributed database all
sites have identical software and are aware
of each other and agree to cooperate in
processing user requests.
 The homogenous system is much easier to
design and manage
 The operating system used , at each
location must be same or compatible.
 The database application used at each
location must be same or compatible.
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8.  In a Heterogeneous distributed database
different sites may use different schema
and software.
 In heterogeneous system, different nodes
may have different hardware & software and
data structures at various nodes or
locations are also incompatible.
 Different computers and operating systems
, database applications or data models may
be used at each of the locations.
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9.  Less danger of a single-point failure . when
one of the computers fails , the workload is
picked up by other workstations.
 Data are also distributed at multiple sites
 The end users is able to access any
available copy of the data and an end users
request is processed by any processor at
the data locations.
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10.  Improved communications . Because local
sites are smaller and located closer to
customers.
 Reduced operating costs . It is more cost-
effective to add workstations to network
than to update a mainframe system.
 Faster data access , faster data processing.
 A distributed database system spreads out
the systems workload by processing data at
several sites.
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11.  Complexity of management and control.
 Applications must recognize data location ,
and they must be able to stitch together
data from various sites.
 Security.
 Increased storage and infrastructure
requirements.
 Multiple copies of data has to be at
different sites , thus an additional disk
storage space will be required.
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12.  A parallel database system is to improve
performance through parallelization of
various operations ,such as loading data
building indexes and evaluating queries.
 The distributions is solely done on the
bases of performance.
 Parallel database improve processing and
input/output speeds by using multiple
CPUs and disks in parallel.
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13.  Fragmentation is a process of division or the
mapping of the tables based on the columns and
rows of data into the smallest unit of data.
 Data that has broken down is still possible to be
combined again with the intention to complete the
data collection using fragmentation.
 Fragmentation is a database server feature that
allows you to control where data is stored at table
level.
 Fragmentation enables you to define groups of
rows or index keys within a table.
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14.  Replication is that we store several copies
of a relation or relation fragment. An entire
relation can be replicated at one or more
sites.
 Similarly , one or more fragment of a
relation can be replicated at other sites.
 For example , if a relation R is fragmented
into R1,R2 and R3 there might be just one
copy of R1 , whereas R2 is replicated at two
other site and R3 is replicated at all sites.
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15.  In a distributed DBMS, a given transaction is
submitted at some one site, but it can access
data at other sites as well.
 When a transaction is submitted at some site,
the transaction manger at the site breaks it
up into a collection of one or more sub-
transaction that execute at different sites ,
submits them to transaction managers at the
others sites and coordinates their activity.
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