In an entity subtype, what can uniquely apply to that entity?

In the context of an entity subtype, attributes that are defined only in the subtype are unique to that entity. This means they are specifically tailored to represent characteristics or properties that distinguish the subtype from its parent entity and other subtypes.

For instance, in a system where there is a general "Vehicle" entity, a "Car" subtype might have specific attributes such as "number of doors" or "trunk size" that do not apply to the more generic "Vehicle" entity or any other subtypes, like "Truck" or "Motorcycle." These unique attributes help to define the specific behaviors and properties relevant to that particular subtype.

While parent entity attributes may be inherited, and other subtype attributes can provide additional context or characteristics, it is the attributes defined exclusively within the subtype that fundamentally differentiate its unique identity and functionality within the framework of the entire entity hierarchy.