Entity Relationship Diagram Example: Simple Order System


ER diagrams symbolically shows the objects (aka entities) within a system. Here is an example. This is an ERD for a simple order system. It covers entities like employee, product, customer, order, payment, etc.

Use this ERD template to get started building your own. Customize the ERD to reflect the entities of your problem. Click Use this Template to start.

What is Entity Relationship Diagram (ERD)?

The Entity-Relationship (ER) diagram (also known as ERD's or ER models) is a classical and popular conceptual data model originally proposed by Peter in 1976. It is a visual representation of different entities within a system and how they relate to each other. Entity Relationship Diagrams are widely used to design relational databases. The entities in the ER schema become tables, attributes and the converted database schema. Since they can be used to visualize database tables and their relationships it's commonly used for database troubleshooting as well.

Steps in designing an Entity-Relationship schema

  • Identify entity types (entity type vs. attribute)
  • Identify relationship types
  • Identify and associate attributes with entity and relationship types
  • Determine attribute domains
  • Determine primary key attributes for entity types
  • Associate (refined) cardinality ratio(s) with relationship types
  • Design generalization /specialization hierarchies including constraints

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