Monday, 19 September 2011

Types of Database

The database may be of different types but there are two generic database architectures. These are:
  • Centralized Database
  • Distributed Database
Centralized Database
                                    A database whose all data is located at a single computer (or site) and multiple users can  access that database is know as centralized database. A centralized database provides an efficient way to access and update data. These databases are usually used in computer network environments. The examples of centralized databases are: 
  • Personal Computer Databases
  • Client/Server Databases
  • Central Computer Databases
(i) Personal Computer Databases
A personal computer database is normally created and maintained by a single user on the personal computer. The personal computer database are commonly used in small business or organization. If there is a need to share data, this database could be stored on a database server in a local area network, so that the multiple user can access and update the database.

(ii) Client/Server Databases
The client/server databases are used in small to medium organization or businesses to share data among multiple users in local area network. The microcomputers are often used in a local area network.

The client/server architecture is designed for the distribution of work on a computer network in which many clients may share the data (or services). Here is an example of  client/server database

(iii) Central Computer Databases
The central computer databases are commonly used in central computers in large organizations. The central computer may be a mainframe or minicomputer. These databases are accessed by a large number of users. The users at remote locations can also access the database using remote terminals and data communication links. 
Distributed Database
Many organizations/departments have sub-offices in different cities and countries. In such cases, the distributed databases are used instead of centralized databases. A distributed database is a single logical database, which is spread physically across computers in multiple locations (such as cities or countries).
The distributed databases are further divided into two categories:
  • Homogeneous Databases
  • Heterogeneous Databases
Homogeneous Databases
The homogeneous database means that the database technology is the same at each of the locations (or sites) and that the data at various locations are also compatible. In a homogeneous system, all nodes use the same hardware and software for the database system.
The following conditions must be satisfied for homogeneous database.
  1. The operating system used at each location must be same or compatible.
  2. The data structures used at each location must be same or compatible.
  3. The database application (or DBMS) used at each location must be same or compatible.
Heterogeneous Databases

The heterogeneous database systems are opposite to homogeneous database systems. In a heterogeneous system, different nodes may have different hardware and software and data structures at various nodes or locations are also compatilbe


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