Different types of database systems on the basis of site location

 Types of database systems on the basis of site location :- 

1. Centralized database system :- 

The centralized database system consists of a single processor together with it's associated data storage devices and other peripherals. It is physically confined to a single location. Data can be accessed from the multiple sites with the use of a computer network while the database is maintained at the central site. 

Disadvantages of centralized database system :- 

• When the central site computer or database system goes down, then every one is blocked from using the system until the system comes back. 
• Communication costs from the terminals to the central site can be expensive. 

2. Parallel database system :- 

Parallel database system architecture consists of a multiple central processing units and data storage disk parallel. Hence, they improve processing and Input/Output speeds. Parallel database systems are used in the application that have to query extremely large database or that have to process an extremely large number of transaction per second. 

Advantages of parallel database system :- 

• Parallel database systems are very useful for the applications that have to query extremely large database or that have to process an extremely large number of transactions per second. 
• In a parallel database system, the throughput and the response time are very high. 

Disadvantages of parallel database system :- 

• In parallel database system, there is a startup cost associated with initiating a single process and the startup time may overshadow the actual processing time affecting speed up adversely. 
• Since process executing in a parallel system often access shared resources, a slowdown may result from interference of each new process as it complete with existing processes for commonly held resources, such as shared data storage disks, system bus and so on. 

3. Distributed database system :- 

A logically interrelated collection of shared data physically distributed over a computer network is called as distributed database and the software systems that permits the management of the distributed database and makes the distribution transparent to users is called as distributed DBMS. 

It consists of a single logical database that is split into a number of fragments. Each fragments is stored on one or more computers under the control of a separate DBMS, with the computers connected by a communication network. In this data is spread across a variety of different database. These are managed by a variety of different DBMS softwares running on a variety of different operating system. These machines are spread geographically and connected together by a variety of communication network's.

Advantages of distributed database system :- 

• Distributed database architecture provides greater efficiency and better performance. 
• A single database can be shared across several distinct client systems. 
• As data volumes and transaction rates increase, users can grow the system incrementally. 
• It causes less impact on ongoing operations when adding new location's.
• Distributed database system provides local autonomy. 

Disadvantages of distributed database system :- 

• Recovery from failure is more complex in distributed database systems than in centralized systems. 

4. Client server DBMS :- 

Client server architecture of database system has two logical components namely client and server. Client are generally personal computers or workstations whereas server is large workstations, mini range computer system or a mainframe computer system. The application and tools of DBMS run on one or more client platforms, while the DBMS software reside on the server. The server computer is called backend and the clients computer is called front end. These server and client computers are connected into a network. The applications and tools act as client of the DBMS, making requests for it's services. The DBMS , in turn, processes these requests and returns the results to the client. Client/server architecture handles the graphical user interface and does computation and other programming of interest to the end user. The server handles parts of the job that are common to many clients. For example, database access and updates.