Entity-Relationship Model

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## TL;DR

The Entity-Relationship (ER) Model (Peter Chen, 1976) is a conceptual data modeling technique. Entities (objects: Customer, Order) have attributes and participate in relationships (places, contains). Cardinality: 1:1, 1:N, M:N. ER diagrams guide database schema design before implementation.

## Core Explanation

Entity: real-world object with independent existence. Weak entity: depends on another entity (OrderItem depends on Order). Relationship: association between entities. Cardinality: `Customer --places--< Order`. Crow's Foot notation is common. ER model maps to relational schema: entities → tables, attributes → columns, relationships → foreign keys. M:N relationships need junction table.

## Further Reading

- [Fundamentals of Database Systems (7th Ed, Elmasri & Navathe)](undefined)

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