Entity:

• definition: representation of a class of an object
• representation: represented as a rectangle, and a name on top
• example: the name of the database

Attributes

• definition: property/properties that describes the entity
• representation: text within the rectangles
• example: column of database

Relationships

• depicted by a line that connects the two entities
• One line means one relationship
• Crow’s foot means many relationships
• Circle means that it’s optional
• mandatory means that there must be a relationship

One to many

erDiagram
    PERSON ||--o{ PASSPORT : id
    PERSON {
        int id
        string name
    }
    PASSPORT {
        int id
        string number
    }

A person can have many passports, or none. A passport however, must be associated with one person.