feature of distributed database

7/31/2019 Feature of Distributed Database

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By : Hussein abed hilal /MSC


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What is the distributed data

baseA distributed database system is a collection of

logically related databases that cooperate in a

transparent manner.

Transparent implies that each user within thesystem may access all of the data within all of the

databases as if they were a single database

There should be location independence i.e.- as

the user is unaware of where the data is located itis possible to move the data from one physical

location to another without affecting the user.


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Data and information

Data : the computer science define the

data as unprocessed data.

Information: this is the data after

processed data that meaning .


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DISTRIBUTED DATABASE

ARCHITECTURE


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Ddb cont

D/BASE

CLIEN

T#1

CLIEN

T#2

CLIEN

T#3

H Di ib d


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Homogenous DistributedDatabase Systems

All sites have identical software They are aware of each other and agree to

cooperate in processing user requests

It appears to user as a single system

H Di ib d


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Heterogeneous DistributedDatabase System

In a heterogeneous distributed databasesystem, at least one of the databases uses

different schemas and software.

A database system having different schema

may cause a major problem for query

processing.

A database system having different software

may cause a major problem for transaction

processing.


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Feature of ddb

Centralized control

Data independence

Reduction of redundancy

Complex physical structure and efficientaccess

Integrity , recovery , and concurrencycontrol

Privacy and security


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Centralized control

It is a one of strongest motivation for

introducing database.

It is possibility to provide centralize

control of information resource.

In ddb the idea of centralized control is

much less emphasized.


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Cont

In ddb we can define administrator whohas responsibility of control on ddb

1. GLOBAL SYSTEM ADMINSTRATOR Who has control of whole database

2. LOCAL SYSTEM ADMINSTRATOR who has responsibility of their respective

local database


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Example

Of center control

Ceterlaziedcontrol

Database 1

database4

database2

Database 3

network network

Localcontrol

Local

control Local

control

Localcontrol


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2-Data independence

It is one of the main introducing of

database.

It is mean that actual organization of

data is transparent to the applicationprogrammer.

Also data independence have the same

importance of traditional of database.


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3-Reduction of Redundancy

In distributed database, however, there areseveral reasons for considering dataredundancy as a desirable feature:

first, the locality of applications can beincreased if the data is replicated at allsites where applications need it,

and second, the availability of the system

can be increased, because a site failuredoes not stop execution of applications at

other sites if the data is replicated.


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Reduction of data

Center control

ddb2 ddb3

ddb4ddb1

Original

data


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4- Complex physical structures

and efficient access

The reason for providing complex

accessing structures is to obtain efficient

access to the data. In distributed database,

complex accessing structures arenot the right tool for efficient access

because cannot be provided by using

physical structures and it is very difficult tobuild and maintain such

structures.


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Complex structure

Distributeddatabase

Site 1

Site 3

Site 2

Site 4

data

Original

data

Part ofdata

Part ofdata


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5- Integrity, recovery, and

concurrency control

In ddb the integrity and recovery and

concurrency to different problem

Transaction and atomic :

It is a sequence of operations which either

are performed or not performed .

For example funds transfer.


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6- Privacy and security

In traditional database, the database

administrator, having centralized control,

can ensure that only authorized access

to the data is performed . But in DDB ,

local administrators are faced with the

same problem as database

administrator in traditional database.


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Advantage and disadvantage of

ddb

Advantages of database distribution

The primary advantage of DDB systems

is the ability to share and access data

in a reliable and efficient manner. The

following is a list of the main

advantages:


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Advantage of DDB

1-Data Sharing and distributed control:

If a number of different sites are

connected , then a user at one site may

be able to access data available atanother site.

2-Reliability and Availability:

If one site fails in a distributed system,the remaining sites may be able to

continue operating .


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Cont

3-Speed of Query processing:

If a query involves data at several sites,

it may be possible to split the query

into sub queries that can be executed in

parallel.


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4-Incremental growth: If an organization grows by adding new,

relatively autonomous organizational

units then the distributed database

approach supports a smoothincremental growth with a minimum

degree of impact on the already existing

units.


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5-Reduced communication

overhead

In a geographically distributed

database, the fact that many

applications are local reduce the

communication overhead with respect toa centralized database. Therefore, the

maximization of the locality of

applications is one of primary objectives

in distributed database design.


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6. Performance considerations

The existence of several processors

results in the increase of performance

through a high degree of parallelism.


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Disadvantage of DDB

The primary disadvantage of distributed

database systems is the added complexity

among the sites. This increased complexity

takes the form of:1.software development cost It is more

difficult to implement a distributed database

system and, thus, more costly.


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Cont

2. Greater potential for bugs Since thesites that comprise the distributedsystem operate in parallel,it is harder to

ensure the correctness of algorithms.The potential exist for extremely subtlebugs .

3. Increased processing overhead.

The exchange of messages and theadditional computation required.


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Cont

Architectural complexity.

Cost.

Security.

Integrity control more difficult.

Lack of standards.

Lack of experience.

Database design more complex.


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The End

feature of distributed database

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