An Entity-Relationship (ER) model is a conceptual data model that describes the structure of a database as entities, attributes and relationships. Its components are:
An entity is a real-world object or concept, drawn as a rectangle, such as a Customer, Product or Order.
An attribute is a property of an entity, drawn as an oval, like a Customer's CustomerID, Name and Email.
A relationship is an association between entities, drawn as a diamond, such as a Customer that "places" an Order.
Cardinality is how many instances of one entity can link to another. A user and their profile are one-to-one, or 1:1. A customer and their orders are one-to-many, or 1:M. Students and courses are many-to-many, or M:N.
Rewriting in plainer words…
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