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Schema and Instance in DBMS

Schema and Instance in DBMS

1. Instances :
Instances are the collection of information stored at a particular moment. The instances can be changed by certain operations as like addition, deletion of data. It may be noted that any search query will not make any kind of changes in the instances.

Example –
Let’s say a table teacher in our database whose name is School, suppose the table has 50 records so the instance of the database has 50 records for now and tomorrow we are going to add another fifty records so tomorrow the instance have total 100 records. This is called an instance.

2. Schema :
Schema is the overall description of the database. The basic structure of how the data will be stored in the database is called schema.

Schema and Instance in DBMS


Schema is of three types: Logical Schema, Physical Schema and view Schema.
  1. Logical Schema – It describes the database designed at logical level.
  2. Physical Schema – It describes the database designed at physical level.
  3. View Schema – It defines the design of the database at the view level.

Example –
Let’s say a table teacher in our database name school, the teacher table require the name, dob, doj in their table so we design a structure as :

Teacher table
name: String
doj: date
dob: date 

Above given is the schema of the table teacher.


Difference between Schema and Instance :


Schema
  • It is the overall description of the database.
  • Schema is same for whole database.
  • Does not change Frequently.
  • Defines the basic structure of the database i.e how the data will be stored in the database.

Instance
  • It is the collection of information stored in a database at a particular moment.
  • Data in instances can be changed using addition, deletion, updation.
  • Changes Frequently.
  • It is the set of Information stored at a particular time.
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