Subclass/Superclass expression
It is possible to associate different entity types by declaring a subclass/superclass relationship. This is done using the extends keyword when declaring
an entity. The following example shows the subclass "Dog" and the superclass "Animal".
entity Animal {
id key
age
location: [latitude, longitude]
}
entity Dog extends Animal {
name
breed
} 💡
Subclass entities can't have a key attribute! This is a semantic restriction of the ER model.
The generated ER diagram will contain the special IsA relationship between the superclass and the subclass.
You can nest subclasses as deep as you want. The generated ER diagrams will follow a tree-like layout.
💡
If an entity extends one of its subclasses, an error will be shown in the Playground.
entity Employee {
name
id key
bday
}
entity Management_Employee extends Employee {}
entity Manager extends Management_Employee {}
entity CEO extends Management_Employee {}
entity Engineer extends Employee {}
entity Senior_Engineer extends Engineer {}
entity Team_Leader extends Senior_Engineer {}
entity Intern extends Engineer {}
entity Secretary extends Employee {
typing_speed
}