Homework #2 FAQ

Question 1

Question: In part (b) what do you mean by the ``object-oriented approach''?
Answer: The text discusses ODL and its translation to relations. However, this is not what we want you to do --- we have deferred ODL for later in the course. Rather, just follow the strategy discussed in class for dealing with isa hierarchies in an ``OO'' style. Recall the beers-and-ales example.

Question 2

Question: In part (f), where do the FD's hold?
Answer: Sorry -- we meant ``which FD's hold in S(A,B,C)?''

Question 3

Question: What is a ``counterexample''?
Answer: We need to see a relation instance in which the given dependencies hold, but the proposed dependency does not.

Question: When looking for 4NF violations, do I have to consider implied MVD's?
Answer: Alas, yes. For FD's and BCNF, we showed that only the given FD's need to be considered. However, for 4NF, you need to consider at least the MVD's X->->Y that follow from the similar-looking FD X->Y.