Three Schema Architecture

Three Schema Architecture is used for the separation of the user application and the physical database. Architecture is defined in three levels:

• Internal level.
• Conceptual level
• External level.

Internal Level defines that how the data is stored, manipulated and organized inside the application itself, which means it describes the physical storage structure of the database. It describes the complete details of data storage and access paths for the database using a physical data model.

Conceptual Level defines data from perspective of the designer (system designer). The conceptual schema hides the details of physical storage structures, but describing entities, data types, relationships, user operations, constraints, etc.

External Level describes only that part of the database in which user is interested and hides the rest of the data base from the user. The part of the database shown to user is known as user view. There can be number of user views.