The Three Schema Architecture, also known as the ANSI/SPARC architecture, is a conceptual framework for organizing the components of a Database Management System (DBMS). It divides the system into three layers or schemas, each with its own distinct purpose and functionality. The three schemas are:

1. External Schema/View Schema/User Schema:

The external schema, also referred to as the view schema or user schema, represents the user's view or perspective of the database. It defines how individual users or applications perceive and access the data. Each external schema corresponds to a specific user or group of users and includes a subset of the entire database schema.

The external schema provides a customized and simplified view of the database, tailored to meet the specific requirements of different users or applications. It defines the tables, views, queries, and other elements necessary for users to interact with the database. The external schema shields the users from the complexity of the underlying database structure and allows them to focus on their specific data needs.

2. Conceptual Schema/Logical Schema:

The conceptual schema, also known as the logical schema, represents the overall logical structure and organization of the entire database. It defines the relationships between various entities, their attributes, and the constraints that govern the data.

The conceptual schema provides a high-level, abstract representation of the database that is independent of any specific implementation or technology. It serves as an intermediary between the external schemas and the physical schema. Changes made to the conceptual schema do not affect the external views, providing a level of data independence.

3. Internal Schema/Physical Schema:

The internal schema, also referred to as the physical schema, represents the physical storage and implementation details of the database on the underlying hardware and operating system. It defines how the data is stored, indexed, and organized on disk.

The internal schema deals with low-level aspects such as file structures, access methods, indexing techniques, and storage optimization. It maps the logical schema to the physical storage structures and specifies the physical representation of the data to achieve optimal performance and storage efficiency.

The Three Schema Architecture separates the logical view (external schema), the conceptual view (conceptual schema), and the physical view (internal schema) of the database. This separation allows for data independence, flexibility, and abstraction. Changes made to one schema do not necessarily require modifications to the other schemas, providing a modular and scalable approach to database design and management.

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