Three schema Architecture

• The three schema architecture is also called ANSI/SPARC architecture or three-level architecture.
• This framework is used to describe the structure of a specific database system.
• The three schema architecture is also used to separate the user applications and physical database.
• The three schema architecture contains three-levels. It breaks the database down into three different categories.

The three-schema architecture is as follows:

In the above diagram:

• It shows the DBMS architecture.
• Mapping is used to transform the request and response between various database levels of architecture.
• Mapping is not good for small DBMS because it takes more time.
• In External / Conceptual mapping, it is necessary to transform the request from external level to conceptual schema.
• In Conceptual / Internal mapping, DBMS transform the request from the conceptual to internal level.

1. Internal Level

• The internal level has an internal schema which describes the physical storage structure of the database.
• The internal schema is also known as a physical schema.
• It uses the physical data model. It is used to define that how the data will be stored in a block.
• The physical level is used to describe complex low-level data structures in detail.

2. Conceptual Level

• The conceptual schema describes the design of a database at the conceptual level. Conceptual level is also known as logical level.
• The conceptual schema describes the structure of the whole database.
• The conceptual level describes what data are to be stored in the database and also describes what relationship exists among those data.
• In the conceptual level, internal details such as an implementation of the data structure are hidden.
• Programmers and database administrators work at this level.

3. External Level

• At the external level, a database contains several schemas that sometimes called as subschema. The subschema is used to describe the different view of the database.
• An external schema is also known as view schema.
• Each view schema describes the database part that a particular user group is interested and hides the remaining database from that user group.
• The view schema describes the end user interaction with database systems.