Schema and Instances

SCHEMA AND INSTANCES

Instance: It is a state of a database schema at any point of time i.e. it’s a snapshot of the database.

 It refers to the record/ collection of data stored in database at any particular moment.

DB Schema: It is an overall design of databases. It can be increased or decreased/ shrinking on the basis of the operations that are happening in a system.

It is a set of storage structure that we create to enter the data.

e.g.-> table represent the schema

           data filled in represents the instances.

Schema remains same throughout a table.

Sub-schema: It is a sub set of the schema.

It refers to an application programmer’s view of the data item types and record items types, which user uses.

 

Note: 4GL (4^th Generation Language)

Provide built in mechanism to create the storage structures and manage the data.

We are not required to make any program here; we just have to invoke the request. In the background, a C program runs and manages the data.