Overview

In this tutorial, we will learn different ER Diagram Cardinality Symbols. The relationships are indicated using lines drawn from one table to another and a symbol at the end which defines the relationship type. ERD acronym stands for Entity-Relationship Diagram.

ER Diagram is an output of the modeling process.

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Cardinality

Cardinality is the maximum number of times an instance of an entity can be associated with instances of another entity s shown in the ER diagrams. Ordinality is the minimum number of times an instance of an entity can be associated with an instance in another entity.

Cardinality Symbols

Cardinality/Ordinality are shown by styling the relationship line and its endpoint with cardinality symbols. Some basic symbols in Crow’s Foot notation are as follows:

 

 

Example

1-to-0 ( or 1) Relationship

1-to-0 ( or 1) Relationship can be represented as shown below. Each instance of Entity A is related to a minimum of zero and a maximum of one instance of Entity B.

 

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