What are two key aspects of an entity subtype?

The correct answer highlights that an entity subtype inherits all attributes from its supertype, which is fundamental in object-oriented design and data modeling. This inheritance allows the subtype to have all the properties and behaviors of the supertype, enabling code reuse and establishing a clear hierarchical relationship between the two.

In entities modeled in a system, the subtype can then extend or override some of these inherited attributes to provide specialized behavior or characteristics specific to that subtype. This mechanism simplifies the overall structure of data management, ensuring that common attributes are defined only once in the supertype while allowing the subtype to build upon that foundation.

The other aspects mentioned do not accurately depict the nature of entity subtypes. For example, not being able to inherit any attributes creates redundancy and violates the principles of effective data modeling. Additionally, claiming that the subtype can only have attributes from its own definition overlooks the core concept of inheritance. The unique identifier may be relevant in some contexts, but it does not directly pertain to the defining characteristics of how subtypes relate to supertypes. Thus, understanding that subtypes inherit all attributes from their supertypes is crucial for anyone working with object-oriented systems or data hierarchies.