Schema VS Instances

Schema VS Instances


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

Schema Diagram: A diagrammatic display of (some aspects of) a database schema.

Schema Construct: A component of the schema or an object within the schema, e.g., STUDENT, COURSE.

Database Instance: The actual data stored in a database at a particular moment in time. Also called database state(or occurrence).



Database Schema Vs. Database State

Database State: Refers to the content of a database at a moment in time.

Initial Database State: Refers to the database when it is loaded

Valid State: A state that satisfies the structure and constraints of the database.
Distinction

The database schema changes very infrequently. The database state changes every time the database is updated.

Schema is also called intension, whereas state is called extension