‘An entity-relationship diagram (ERD) is a graphical representation of an information system that shows the relationship between people, objects, places, concepts or events within that system. An ERD is a data modeling technique that can help define business processes and can be used as the foundation for a relational database.’ [http://searchcrm.techtarget.com/definition/entity-relationship-diagram]
Information that is needed from users such as:
This helps to identify the users so when they contribute/login/post on a a site this information can help to identify the user.
Entities are objects or concepts that can have data stored in them, the relationship between those entities is what is displayed in a ERD.
The three main relationships are:
- One-to-one (1:1). For example, if each customer in a database is associated with one mailing address.
- 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.
- Many-to-many (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.