Three levels of database architecture:
Following are the three levels of database architecture,
Fig: Three levels database architecture
In the above diagram,
It shows the architecture of DBMS.
Mapping is the process of transforming request response between various database levels of architecture.
Mapping is not good for small database, because it takes more time.
In External / Conceptual mapping, DBMS transforms a request on an external schema against the conceptual schema.
In Conceptual / Internal mapping, it is necessary to transform the request from the conceptual to internal levels.
1. Physical Level :
Physical level describes the physical storage structure of data in database.
This level is very close to physical storage of data.
At lowest level, it is stored in the form of bits with the physical addresses on the secondary storage device.
At highest level, it can be viewed in the form of files.
The internal schema defines the various stored data types.
It uses a physical data model.
2. Conceptual Level
Conceptual level describes the structure of the whole database for a group of users.
It is also called as the data model.
Conceptual schema is a representation of the entire content of the database.
These schema contains all the information to build relevant external records.
- It hides the internal details of physical storage.
3. External Level
External level is related to the data which is viewed by individual end users.
This level includes a no. of user views or external schemas.
This level is closest to the user.
External view describes the segment of the database that is required for a particular user group and hides the rest of the database from that user group.