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 .
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.
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.
Combining examples and defining relationships between them :
Reading Method :
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.