Functional Dependency Reduction

Question

I'm supposed to find the minimal cover for this set of FD's. Please let me know if my answer is correct.

My answer:

score 1 · Accepted Answer · answered Aug 03 '11 at 02:49

1

It seem to me that the first one is not correct:

answered Aug 03 '11 at 02:49

zw324

So should I delete that dependency and leave X in 2. and 3.? Also should Y be deleted from 5. since XZ->Y->B? – Leif Aug 03 '11 at 02:51
@Leif I think so. You can look at the slide 12 (the rest might be helpful too) here: http://www.doc.ic.ac.uk/~pjm/db/fd-lecture.pdf – zw324 Aug 03 '11 at 02:54
1. XZ->Y 2. XZ->B 3. YA->C 4. A->G 5. C->W 6. B->G I'm just confused about whether or not Y can be deleted from 4. if the implication is derived from XZ.. I'm thinking it should stay. – Leif Aug 03 '11 at 03:02
@Leif I think so too, since if Y is deleted then the dependency will not be able to construct from the set. Double check if this is homework, though:) – zw324 Aug 03 '11 at 03:07

score 0 · Answer 2 · answered Aug 04 '11 at 15:16

X->Z (deleted Z attribute, trivial FD)

The trivial part of XZ->Z is Z->Z. I don't think you can derive X->Z from XZ->Z.

If #1 is wrong, this #2 and #3 are also wrong.

Numbers 4-7 in your answer are right. (Your answer that's inside your question, that is.)

From your comment to Ziyao Wei,

XZ->Y 2. XZ->B 3. YA->C 4. A->G 5. C->W 6. B->G

Number 4 is wrong. Correct it, and you've found the minimal cover. Also, you said

I'm just confused about whether or not Y can be deleted from 4. if the implication is derived from XZ.

If you post your reasoning--how you derived A->G from XZ->Y and YA->C--then someone can probably show you where your reasoning went astray.

2 Answers2