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Feature of distributed database

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Feature of distributed database Powered By Docstoc
					By : Hussein abed hilal /MSC
What is the distributed data base
 A distributed database system is a collection of
    logically related databases that cooperate in a
    transparent manner.

   Transparent implies that each user within the
    system 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 it
    is possible to move the data from one physical
    location to another without affecting the user.
Data and information
   Data : the computer science define the
    data as unprocessed data.



   Information: this is the data after
    processed “ data that meaning “.
DISTRIBUTED DATABASE
ARCHITECTURE
Ddb cont’

 CLIEN
   T#1
            D/BASE


 CLIEN
   T#2



 CLIEN
   T#3
Homogenous Distributed
Database 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
Heterogeneous Distributed
Database System
   In a heterogeneous distributed database
   system, 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.
Feature of ddb

 Centralized control
 Data independence
 Reduction of redundancy
 Complex physical structure and efficient
  access
 Integrity , recovery , and concurrency
  control
 Privacy and security
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.
Cont’
    In ddb we can define administrator who
     has 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
Database 1
                 Example         database2
             Of center control
   Local                           Local
  control                         control




 network        Ceterlazied       network
                  control


  control                         control
   Local                           Local




Database 3                       database4
2-Data independence
 It is one of the main introducing of
  database.
 It is mean that actual organization of
  data is transparent to the application
  programmer.
 Also data independence have the same
  importance of traditional of database.
3-Reduction of Redundancy
 In distributed database, however, there are
  several reasons for considering data
  redundancy as a desirable feature:
 first, the locality of applications can be
  increased if the data is replicated at all
  sites where applications need it,
 and second, the availability of the system
  can be increased, because a site failure
  does not stop execution of applications at
  other sites if the data is replicated.
       Reduction of data


ddb2                         ddb3




            Center control




ddb1                         ddb4


               Original
                data
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 are
    not the right tool for efficient access
    because cannot be provided by using
    physical structures and it is very difficult to
    build and maintain such
    structures.
                   Complex structure


                                       Site 2   Original
          Site 1
 data                                            data



                        Distributed
                        database




Part of                                         Part of
          Site 4                       Site 3
 data                                            data
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”.
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.
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:
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 at
  another site.
2-Reliability and Availability:
   If one site fails in a distributed system,
   the remaining sites may be able to
   continue operating .
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.
4-Incremental growth:

   If an organization grows by adding new,
    relatively autonomous organizational
    units then the distributed database
    approach       supports    a     smooth
    incremental growth with a minimum
    degree of impact on the already existing
    units.
5-Reduced communication
overhead
  In     a    geographically    distributed
 database,      the   fact   that     many
 applications are local reduce the
 communication overhead with respect to
 a centralized database. Therefore, the
 maximization      of   the   locality   of
 applications is one of primary objectives
 in distributed database design.
6. Performance considerations
 The existence of several processors
 results in the increase of performance
 through a high degree of parallelism.
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.
Cont’
2. Greater potential for bugs Since the
   sites that comprise the distributed
   system operate in parallel,it is harder to
   ensure the correctness of algorithms.
   The potential exist for extremely subtle
   bugs .
3. Increased processing overhead.
   The exchange of messages and the
   additional computation required.
Cont’
   Architectural complexity.

   Cost.

   Security.

   Integrity control more difficult.

   Lack of standards.

   Lack of experience.

   Database design more complex.
The End

				
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posted:11/2/2012
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