COS 425
                                  Homework # 3
                             100 pts, 25 pts each.

                        Due: Thursday, March 14th, 1996.


1) (a) Compute the closure, F+, of the following set F of FDs for relation
       schema R=(A,B,C,D,E).
               A  -> BC
               CD -> E
               B  -> D
               E  -> A

    (b) Compute the closure for each attribute (e.g., A+, B+, ...).

    (C) What are all the candidate keys?

2) Using R and F from (1), show that the decomposition of R1(A,B,C) and 
   R2(A,D,E) is lossless. Is it FD-preserving?


3) Using R and F from (1), show that the decomposition of R1(A,B,C) and 
   R2(C,D,E) is not lossless. 


4) Given the schema on R, where R=(A, B, C, D), and the set F of 
   FDs, where F is:
          AB -> C | D
          C  -> B

   (A) What normal form is R in?

   (B) Put R in BCNF (so obviously (A) is not BCNF).

   (C) Is the BCNF of R FD-preserving?