Entity relationship diagram
Definition
An entity relationship diagram (ERD) is a data modeling diagram that shows the entities (things the system tracks), their attributes, and the relationships between them, including cardinality (one-to-one, one-to-many, many-to-many).
Peter Chen introduced ERDs in a 1976 paper that became one of the most cited in computer science. The core insight was that any data domain could be described as entities, attributes, and relationships — and that drawing this structure before writing SQL saved enormous rework.
An ERD has three components. Entities are the 'nouns' of the system: Customer, Order, Product, Invoice. Attributes describe each entity: Customer has name, email, created_at. Relationships connect entities: a Customer places many Orders; an Order contains many Products.
Cardinality notation varies — Chen notation uses '1' and 'N' or 'M'; Crow's Foot notation (common in database tools) uses line endings that look like crow's feet for 'many.' Both appear on whiteboards.
Engineering teams draw ERDs at the start of a project to design the database schema, during refactoring sessions to understand what already exists, and during architecture reviews when a new feature touches the data model. BoardSnap AI reads the entity boxes, attribute lists, and relationship lines from the photo to produce a summary of the data model.
Examples
- E-commerce ERD: Customer (1) — places — (many) Order (many) — contains — (many) Product
- Blog platform: User (1) — writes — (many) Post (1) — has — (many) Comment
- SaaS app: Organization (1) — has — (many) Workspace (1) — contains — (many) User
- Inventory system: Supplier (many) — supplies — (many) Product (1) — stored in — (many) Location
Related terms
Snap a entity relationship diagram. Ship its actions.
BoardSnap turns any whiteboard — including this one — into a summary and action plan.