In a distributed database management system, the database is not stored at a single location. Rather, it may be stored in multiple computers at the same place or geographically spread far away. Despite all this, the distributed database appears as a single database to the user. A diagram to better explain this is as follows:
As seen in the figure, the components of the distributed database can be in multiple locations such as India, Canada, Australia, etc. However, this is transparent to the user i.e the database appears as a single entity.
The following are the types of Distributed Database Management System:
In a homogeneous DDBMS, the database management systems across all locations are uniform and based on the same data model. These database management systems are much easier to handle and the database can even be scaled if required.
In heterogeneous DDBMS, the database management systems across different locations may be based on different data models such as relational, hierarchical, object oriented etc. This type of database systems are a result of later integration of individual database systems. They are quite complicated and difficult to manage.
The distributed database can have the data arranged according to different levels of transparency i.e data with different transparency levels can be stored at different locations.