Entities
Business objects that usually become database tables, such as users, orders, and products.
ERD diagram guide
ERD diagram guide for database design examples and tools
Learn how ERD diagrams document tables, columns, keys, and relationships, then use practical database design examples and ErdForge's online ERD workspace to turn requirements into a data model.
Definition
What is an ERD diagram?
ERD stands for Entity Relationship Diagram. It shows the data objects a service manages and the relationships between them, helping developers decide which tables are needed and how records reference each other.
Elements
Core ERD elements
Attributes
Column-level data including names, types, required flags, defaults, and uniqueness.
Identifiers
Primary keys and foreign keys that make rows and relationships reliable.
Relationships
The direction and cardinality between entities, such as one-to-many or optional one-to-one.
Workflow
ERD design workflow
Extract entity candidates from requirements
List nouns the service must store, then remove duplicates or overly broad candidates.
Define attributes and keys
Add columns such as id, status, and created_at, then mark primary keys, foreign keys, uniqueness, and nullability.
Connect relationships and cardinality
Represent rules such as whether one user can have many orders or whether each order must have a user.
Review normalization and query patterns
Check repeated columns, many-to-many relationships, derived values, and the flows your API will query often.
Keep review history with the team
Treat the ERD as a living design document that changes with the product.
Example
Commerce order ERD example
A small commerce domain can start with users, orders, order_items, and products. Instead of connecting orders and products directly as many-to-many, use an order_items table to preserve quantity and price-at-order data.
ErdForge
Using ErdForge
ErdForge gives you a canvas for ERD editing, team sharing, Oracle/PostgreSQL/MySQL/MariaDB/SQLite type options, JSON and SQL export, and MCP integration for AI-assisted diagram drafts.