Discussion
When mapping a supertype/subtype relationship which of the following is true?
Answer: A
Correct answer: The supertype primary key is assigned to each subtype.
Each subtype becomes a relation whose primary key is the supertype’s primary key, which is also a foreign key referring back to it. This is what makes the subtype row and the supertype row the same entity seen twice, and it is why a subtype instance cannot exist without its supertype instance.
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