Three schema Architecture | Internal Level | Conceptual Level | External Level

Three schema Architecture

DBMS Three schema Architecture

• Internal Level 
• Conceptual Level 
• External Level 

Three schema Architecture 

• 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 user applications and physical databases.
• There are three levels in the three schema architecture. It breaks the database into three different categories.

The three-schema architecture is as follows:

In the above diagram:

• It shows the DBMS architecture.
• Mapping is used to convert request and response between different database levels of the architecture.
• Mapping is not good for small DBMS as it takes more time.
• External / conceptual mapping, it is necessary to convert the link from the external level to the conceptual schema.
• Conceptual / internal mapping converts DBMS requests from conceptual to internal level.

1. Internal Level

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

2. Conceptual Level

• Conceptual schema describes the design of a database at the conceptual level. The conceptual level is also known as the logical level.
• This schema describes the structure of the entire database.
• Conceptual level tells what data will be stored in the database and also tells what are the relationships between those data.
• In the conceptual level, the internal details such as the structure of the data implementation are hidden.
• Programmers and database administrators are working on such level.

3. External Level

• At the external level, a database consists of several schemas which are sometimes called subschemas. Subschema is used to describe different views of the database.
• External schema is also known as view schema.
• A view schema describes the database portion that a particular user group is interested in and hides the remaining databases from that user group.
• The View schema describes the end user interaction with the database system.