What is cardinality in a database ERD diagram, and how is it represented?

Answered on : 2024-01-23

Sources

All about ER model cardinality with examples

gleek.io

1

Entity-Relationship Diagram Symbols and Notation

lucidchart.com

2

What is Entity Relationship Diagram (ERD)?

visual-paradigm.com

3

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Cardinality in an Entity-Relationship Diagram (ERD) defines the possible number of occurrences in one entity associated with the number of occurrences in another. It indicates the relationships' numerical attributes. Here's a concise explanation:

1. **Definition:** Cardinality is the count of times one entity can (or must) associate with each occurrence of another entity[6].

2. **Representation:**

- Cardinalities are numerical values expressing the degree of association between two entities in a relationship[4].

- Common cardinal relationships include one-to-one, one-to-many (or many-to-one), and many-to-many[8].

3. **Example:** In a team-player relationship, a cardinality of "ONE team has MANY players" signifies a one-to-many relationship[3].

Understanding cardinality is crucial for designing effective database relationships in ERD diagrams.

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