Schema & Instance

Schema

• A schema is a description of the data interface to the database (i.e. how the data is organized).

• Schema is the overall design of a database.

• It is the skeleton structure of the database.

• It represents the logical view of the entire database.

• A schema contains schema objects:- table, columns, data types, foreign key, primary key, views, stored procedure, etc.

• It represents database objects and relationships with visual diagrams.

• It is designed by database designers to help programmers.

• The process of database creation is called data modeling.

• A schema diagram can display only some aspects of a schema like the name of record type, data type, and constraints. Other aspects can't be specified through the schema diagram.

Instance

• A database instance is a database (real data) that conforms to a given schema.

• Data at a particular moment of time is called the instance of the database.