#schema #instance #rdbms
what is the Difference between schema and instance in dbms?
Schemainstance distinction in RDBMS
Example
Lets say we have a bus, and there are certain number of seats, and capacity of passengers that the bus can carry.
This seat structure is the schema. This does NOT change frequently.
But the seating arrangement of people might change at different instances of time.
The seating arrangement at a particular instance of time represents instance.
What are we going to learn?
We will learn:
Difference between schema and instance
Naming convention of schema and instance in programming language
Example of relation instance and schema


Difference between schema and instance
There are 2 schemas and instances:
Database Relation
Naming convention of schema and instance in programming language
In programming language we Name relation schema like a type definition, i.e. Starting with a capital letter and remaining all small letters.
And we name relation instance like a variable, with all small letters.
Example
So suppose we have a relation “account” and we have to denote it’s schema, it will look like this:
Accountschema = (accountnumber, branchname, balance)
*Whenever we want to say relation instance, we simply call it relation.

Example
A relation instance is like a variable in programming language.
Just like the variable, the value of relation instance changes with time as the relation is updated.
SO, to denote that account is a relation on Accountschema, we write it like this:
account(Accountschema)
Example