A distributed database system (DDBS) is a database physical stored on several computer systems across several sites connected via communication network. Each site is typically managed by a DBMS that is capable of running independently of the other sites.
In other words each site is a data base system site in its own right and its own local users, its own local DBMS and its own local data communication s manager.
• Databases in the collection are logically interrelated with each other. Often they represent a single logical database.
• Data is physically stored across multiple sites. Data in each site can be managed by a DBMS independent of the other sites.
• The processors in the sites are connected via a network. They do not have any multiprocessor configuration.
• A distributed database is not a loosely connected file system.
• A distributed database incorporates transaction processing, but it is not synonymous with a transaction processing system.
Advantages of Distributed Databases: Following are the advantages of distributed databases.
1. Modular Development − If the system needs to be expanded to new locations or new units, in centralized database systems, the action requires substantial efforts and disruption in the existing functioning. However, in distributed databases, the work simply requires adding new computers and local data to the new site and finally connecting them to the distributed system, with no interruption in current functions.
2. More Reliable − In case of database failures, the total system of centralized databases comes to a halt. However, in distributed systems, when a component fails, the functioning of the system continues may be at a reduced performance. Hence DDBMS is more reliable.
3. Better Response − If data is distributed in an efficient manner, then user requests can be met from local data itself, thus providing faster response. On the other hand, in centralized systems, all queries have to pass through the central computer for processing, which increases the response time.
4. Lower Communication Cost − In distributed database systems, if data is located locally where it is mostly used, then the communication costs for data manipulation can be minimized. This is not feasible in centralized systems.