Entity-Relationship Diagram

“An entity-relationship diagram is a visual representation of an information system. That shows a relationship between people, objects, places, concepts or events within that system.” – Margaret Rouse

This data modelling technique is commonly used within businesses that helps structure a process.

There are three main components of an ERD are the entities which are objects or concepts that can have data stored about them, the relationship between those entities, and the cardinality, which defines that relationship in terms of numbers. (2014, Rouse)

The three main cardinal relationships are:

  • One-to-one (1:1). For example, if each customer in a database is associated with one mailing address. (2014, Rouse)
  • One-to-many (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. (2014, Rouse)
  • Many-to-many (M:N). For example, at a company where all call centre agents work with multiple customers, each agent is associated with multiple customers, and multiple customers might also be associated with multiple agents. (2014, Rouse)


Rouse, Margaret. ‘What Is Entity Relationship Diagram? – Definition From Whatis.Com’.SearchCRM. N.p., 2014. Web. 19 Feb. 2015.

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