Thursday, March 2, 2017

Explain one-to-one relationship with example

Explain one-to-one relationship with example, one-to-one relationship in ER diagram, Define one-to-one relationship

One-to-one relationship

If an entity [a record] of one entity set is associated with maximum of one entity of the other entity set, then the relationship type is said to be one-to-one.

When we would say the relationship is one-to-one?
Assume two entity sets A and B. The relationship between A and B is one-to-one if and only if “an entity in A is associated with only one entity (record) in B and an entity in B is associated with only one entity (record) in A”.
If we put in simpler terms, entity set B is the one side for A and entity set A is the one side for B.
Let us assume a database for Airline Reservation System. Further assume that there are two entity sets Passengers and Boarding_Pass to model the passenger details and the flight tickets details respectively. If it is decided to issue each passenger a boarding pass, then the relationship between the entity sets Passengers and Boarding_Pass will be One-to-one.
As shown in the figure below, each passenger is allotted only one seat. Each passenger entity is associated with exactly one boarding_pass entity.

Sample one-to-one relationships showing links between entities of two entity sets

Observe carefully from the above figure the following;

  • Each passenger is allotted with exactly one seat. [look from passenger to boarding_pass]

  • Also, each seat is allotted to exactly one passenger. [look from boarding_pass to passenger]

The ER diagram for this is as follows;

One-to-one relationship between two entity sets Passengers and Boarding_Pass

Look at the ERD carefully. Arrow head is used in either side of the relationship Given. It indicates, one passenger for one boarding_pass, also one boarding_pass for one passenger.


1 comment:

  1. anyone can draw a ER Diagram of this example
    A class is held in one room but a room has many classes.


Featured Content

Multiple choice questions in Natural Language Processing Home

MCQ in Natural Language Processing, Quiz questions with answers in NLP, Top interview questions in NLP with answers Multiple Choice Que...

All time most popular contents

data recovery