Explain Three-Schema Architecture of database

Three levels of database architecture:

Following are the three levels of database architecture,

  1. Physical Level

  2. Conceptual Level

  3. External Level

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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.

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