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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.
What Are Instances And Schemas in DBMS ? Reviewed by Hardik Pandya on 5:31:00 PM Rating: 5

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