Entity Relationship Diagram

Definition

An Entity Relationship Diagram (ERD) models the data entities relevant to a business domain, the attributes that describe each entity, and the relationships between entities — including cardinality (one-to-one, one-to-many, many-to-many). ERDs provide a structural blueprint of how information in a system relates and connects.

Inputs

• Identified data entities relevant to the business domain or system (e.g. Customer, Order, Product)
• Knowledge of the attributes each entity holds and how entities relate to one another

Outputs

• A diagram showing entities, their key attributes, and the relationships and cardinality between them
• A structural reference used to design databases, validate data requirements, and identify missing or duplicate data concepts

When to Use

• Defining or validating the data structure underlying a system or solution
• Multiple entities have meaningful relationships that affect how the system must behave (e.g. a customer can have many orders, but an order belongs to one customer)
• Communicating data requirements clearly between business stakeholders and technical/database teams

When Not to Use

• Systems or features with no meaningful data relationships to model (e.g. a single standalone configuration setting)
• Very early discovery work where the data model is still too undefined to diagram usefully