## Introduction

Formally, we know a **relation** is a subset of a Cartesian Products of sets. i.e $ R \in ( A X B ) $

For Example.

$$ A = \{ 1, 3 \} , B = \{ 2, 5 \} $$

Cartesian Product of set A and B will be

$$ P = \{ (1,2),(3,2),(1,5),(3,5)\} $$

Out of that there are three pair that observe the $ < $ relationship

$$ R = \{ (1,2), (1,5), (3,5)\} $$

Or we can 1 is related to 5 by relation R ($<$)

In real world we name each relation by name which makes sense for others,

and with each relation name we associate its schema - which is a sequence of

attributes(i.e a column in Table)

For Example for above set we have a relation of $ R (A,B) $ which we can write more as

- lessthan(A,B)

In Real world we represent the relation in Table with attributes as column - Student(Id, FirstN, LastN)

ID | FirstN | LastN |
---|---|---|

101 | John | Deo |

102 | Jane | Deo |

103 | Jhonny | Deo |

Note : Attributes names in relation schema must be different