Schema

Schema

A description of data in terms of a data model is called the schema

Every relation has a schema, which describes the name of the relation, name of each attribute (field or column),  and the type of each column.
e.g.
Students(sid: string, name: string, login: string,age: integer, gpa: real)

Schemas versus 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).