Database Schema

Database Schema

The description of a database. Includes
descriptions of the database structure and the constraints that should hold on the database.

DBMS Defines schemas at three levels :

- Internal schema at the internal level to describe data
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. 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.

Database Instance: The actual data stored in a database at a particular moment in time. also called database state