Three levels of database architecture:

Following are the three levels of database architecture,

1. Physical Level

2. Conceptual Level

3. External Level

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.