The following questions are taken from the course's required textbook and do not belong to me - H. G. Molina, J. Ullman, J. Widom : Database Systems The Complete Book, Pearson/Prentice Hall 2009.
Q1: Page 77 - Example 3.8
Consider R(A, B, C, D, E, F) and S = {AB -> C, BC -> D, D -> E, CF -> B}. What is the closure of {A, B}?Q2: Page 77 - Example 3.9
Do the following functional dependencies follow from S in Example 3.8?
- AB -> D
- D -> A
Q3: Page 83 - Exercise 3.2.2
Consider the following schemas and set of functional dependencies:
- S(A, B, C, D) with FDs A -> B, B -> C, B -> D
- T(A, B, C, D) with FDs AB -> C, BC -> D, CD -> A, AD -> B
- U(A, B, C, D) with FDs A -> B, B -> C, C -> D, D -> A
- What are all the nontrivial FD’s that follow from the given FD’s? You should restrict yourself to FD’s with single attributes on the right side.
- What are all the keys of R?
- What are all the superkeys for R that are not keys?
Q4: Page 85 - Exercise 3.2.10
Suppose we have relation R(A ,B ,C ,D ,E), with some set of FDs, and we wish to project those FDs onto relation S(A, B, C). Give the FDs that hold in S if the FDs for R are:
- AB -> DE, C -> E, D -> C, E -> A
- A -> D, BD -> E, AC -> E, DE -> B
- AB -> D, AC -> E, BC -> D, D -> A, E -> B
- A -> B, B -> C, C -> D, D -> E, E -> A