How The Distributed Database Different From Centralized Database?

Definition of a Distributed database http://www.webopedia.com/TERM/D/distributed_database.html "A database that consists of two or more data files located at different sites on a computer network. Because the database is distributed, different users can access it without interfering with one another. However, the DBMS must periodically synchronize the scattered databases to make sure that they all have consistent data" Here you can find a really good text about Distributed Databases: Scale Up in Distributed Databases http://www.cs.rpi.edu/~noel/distr_scaleup/distributed.html I have extracted some key phrases on Why use a distributed database over a centralized one: "A big advantage of distributed DBMSs over centralized ones is that of scalability. Growth can be sustained more gracefully in a distributed system." "Local autonomy is another reason for a business to implement a DDBMS. Since the nature of today's applications usually require data in geographic areas that are often decentralized, it often makes sense to implement a distributed system. In this way, data can physically reside nearest to where it is most often accessed, thus providing users with local control of data that they interact with." "Another reason why one might want to consider a parallel architecture is to improve reliability and availability of the data in a scalable system. In a distributed system, with some careful tact, it is possible to access some, or possibly all of the data in a failure mode if there is sufficient data replication." Another good paper about Distributed Database Systems: Emerging Technologies for Developing Distributed Database Systems http://bridge.ecn.purdue.edu/~yiguo/dropbox/w2000.pdf And here are the solutions to a test about distributed Database Systems, very useful to say in a few words what a DDBMS is: Distributed Database Systems - Solutions http://www.cs.jcu.edu.au/Subjects/cp3020/1997/Tutorials/tute8_soln.html Major features of a DDB are:     * Data stored at a number of sites, each site logically single processor     * Sites are interconnected by a network rather than a multiprocessor configuration     * DDB is logically a single database (although each site is a database site)     * DDBMS has full functionality of a DBMS     * To the user, the distributed database system should appear exactly like a non-distributed database system. Advantages of distributed database systems are:     * local autonomy (in enterprises that are distributed already)     * improved performance (since data is stored close to where needed and a query may be split over several sites and executed in parallel)     * improved reliability/availability (should one site go down)     * economics     * expandability     * shareability Disadvantages of distributed database systems are:     * complexity (greater potential for bugs in software)     * cost (software development can be much more       complex and therefore costly. Also, exchange       of messages and additional computations       involve increased overheads)     * distribution of control (no single database administrator controls the DDB)     * security (since the system is distributed the chances of security lapses are greater)     * difficult to change (since all sites have control of their own sites)     * lack of experience (enough experience is not available in developing distributed systems)

"The database is stored on several computers.The computers in a distributed system communicate with another through various communication media,such as high speed networks or telephone lines and they do not share main memory or disks." "Centralized system a modern,general purpose computer system consists of one to a few CPUs and a number of device controllers that are connected through a common bus that provides access to shared memory and the CPUs have local cache memories."

Centralized database controlled by dba and importants secure informations are stored in the database. Whereas in a distributed database replica of data available in multiple sites.So loss of data in one site could not be affect the  total system.

Distributed databases can be defined as a collection of multiple, logically interrelated databases distributed over a computer network. And distributed database management system (DDBMS) manages the distributed databases and makes this distribution transparent to the user. All the database must be logically related that are managed by DDBMS (distributed database management system). The distributed databases are not just the 'collection of files' stored individually at different network nodes. Rather to form DDBS (distributed databases) all the files should be logically related and there should be structures among those files. In the case of distributed databases, data must be physically distributed across the network nodes otherwise they will simply be separate databases not 'distributed databases'. Sometimes the multiprocessor system is also considered as distributed data processing systems but in fact it is not true. As multiprocessor system may use either 'shared-nothing architecture' or 'shared-everything architecture'. Shared-nothing architecture system may work like distributed computing environment but it is not. because in distributed environment there may be heterogeneity of hardware as well as operating system at different sites in network which is not the case in multiprocessor systems. Thus for distributed databases data must be distributed over network nodes. While centralized databases are managed by DBMS, and no data distribution is done in this case.

1. Differentiate between features of the centralized database and distributed Databases

The centralized database has maintain all the resource, if any client would like to need to use that resource ,that user ask to server that is centralized database. This database provide response to respected client by using distributed database.... By Gnanasekaran.s

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