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.