What Are Instances And Schemas in DBMS ?

Instance : Collection of information stored in the database at a particular (instance of time) moment is called an instance of the database.

Schema : The overall design of the database is called the database schemas.

Analogy to the concept  of data types, variables, and values in programming language :

consider a structure in c.

structure customer
{
     char customer_name[50];
     char social_security[50];
     char customer_street[50];
     char customer_city[50];
}cust;

Here, cust is a variable of type customer structure. A database schema corresponds to the programming language type definition.

A variable of a given type has a value at a given instance. The value of the variable in programming languages corresponds to an instance of a database schema.

Database supports three database schemas:

1. Physical Schema : It is at he lowest level. i.e. at Physical level.

2. Logical Schema : It is the next or intermediate level i.e. at Logical Level.

3. Sub-Schema : It is at the highest level i.e. at the view level.