Three-Schema Architecture

Three-Schema Architecture


Proposed to support DBMS characteristics of:

Program-data independence.

Support of multiple views of the data.

Use of a catalog to store the database description (schema).

Internal schema at the internal level to describe physical storage structures and access paths. Typically uses a physical data model.

Conceptual schema at the conceptual level to describe the structure and constraints for the whole database for a community of users. Uses a conceptual or an implementation data model.

External schemas at the external level to describe the various user views. Usually uses the same data model as the conceptual level.