In a supertype/subtype hierarchy, where should attributes be assigned to maximize reuse and proper inheritance?

Introduction / Context:
Supertype/subtype modeling avoids duplication by placing shared characteristics at common ancestors. Correct placement improves integrity and reduces redundancy.

Given Data / Assumptions:

• Supertypes hold attributes common to all subtypes.
• Subtypes add only attributes unique to their specialization.

Concept / Approach:
Assign attributes as high as possible in the hierarchy (the lowest common ancestor) so all relevant subtypes inherit them. Unique attributes stay with the specific subtype that requires them.

Step-by-Step Solution:

Verification / Alternative check:
Normalization and inheritance principles both recommend elevating shared properties to the highest logical level.

Why Other Options Are Wrong:
Assigning low: Duplicates data across subtypes.
Higher levels inheriting from subtypes: Reverses inheritance.
Immediate-only rule: Misstates how general attributes propagate.

Common Pitfalls:
Copying the same attribute into multiple subtypes instead of using the supertype.

Final Answer:
Attributes are assigned at the highest logical level.