# Crow’s Foot Notation

When we design a database management system , we set some basic rules and define a limit and relation between different entities . In other words , we decide in what capacity the entities will interact each other.  Cardinality & Modality are two concepts that take care of these rules. Hence , today’s article is about how to link entities with each other.Crow’s Foot Notation is used to represent them.

Supposedly , you landed here directly and need to go through what i am saying. Go through these articles first and then come back .

If you are not a beginner  , then please continue . After this article , we will learn how to do an ERD  ( Entity-Relation Diagram ) because we have covered every aspect of the terms and concepts we have to use in ERD .

## Cardinality

What will be the maximum relationship between entities . This sometimes is also referred as mandatory part of relationship. Let’s clear this up with an example.

If we talk about a relation between Student and University. I can say that Awais studied in a Government College University Lahore , now by rule Awais can be a student of only one university at max. Right? What about University? University can have one and more than one students.

Relationship between Student-University , hence is one-to-many.  What is the maximum relationship between two entities? It will either be one or many.

## Modality

What will be the minimum relationship between entities. This is referred as optional part of relationship that entities can and cannot have .  Taking another example of Awais’ University.

Awais’s University gives out Annual Scholarships to its brightest and sharpest . Relationship between Student and Scholarship could be , any student may or may not have a Scholarship , but  Scholarship  will be given to at least one student .  So Student may or may not have a Scholarship but Scholarship will have one or many students.

#### Representation :

Combining examples and defining relationships between them :

Student-University : Read the relationship from Student to University . Cardinality and Modality symbols will be on University side. One Student at max in One University and at least in One University.

University-Student : One University can have more than one Student and at least one .

Comment below the rest of the relationships , if you understand the concept here.

Relationships between entities are defined by cardinalities and modalities . Symbol at right side for maximum and left for minimum.

## Crow’s Foot Notation Visually

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Next Article , will be on an ERD diagram . How to create one and translation of a case study into ERD.  Very exciting stuff. Subscribe for more articles . See you next time.