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Data & Analytics · Foundational

Entity-Relationship Diagram (ERD)

A diagram that shows entities, their attributes and the relationships between them, used to design databases.

Definition

ERDs visualize a data model at the conceptual, logical or physical level. Entities become tables, attributes become columns and relationships become foreign keys. Notations include Chen and Crow's Foot, which shows cardinality and optionality at each end of a relationship line.

Example

An ERD showing Customer 1 --< many Order >-- many Product through an OrderLine entity.

Exam tip

Know how to read cardinality symbols: a crow's foot means many, a bar means one and a circle means zero (optional).

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