ER Diagram

An entity-relationship diagram (ERD) is a data modeling technique that graphically illustrates an information system’s entities and the relationships between those entities. An ERD is a conceptual and representational model of data used to represent the entity framework infrastructure.

The elements of an ERD are:

• Entities
• Relationships
• Attributes

Relationships Between Entities

A relationship is how the data is shared between entities. There are three types of relationships between entities:

1. A one-to-one relationship (1:1). For example, if each customer in a database is associated with one mailing address.
2. A one-to-many relationship (1:M). For example, a single customer might place an order for multiple products. The customer is associated with multiple entities, but all those entities have a single connection back to the same customer.
3. A many-to-many relationship (M:N). For example, at a company where all call center agents work with multiple customers, each agent is associated with multiple customers, and multiple customers might also be associated with multiple agents.