Test by Bikram | Databases | Test 2 | Question: 12

Question

Consider a table $R (A,B,C,D,E)$ where the functional dependencies are:

$A \rightarrow B$

$B \rightarrow C$

$D \rightarrow E$

Table is decomposed as $D=\{ R1 (A,B), \ R2 (B,C), \ R3 (D,E) \}$

Then, the decomposition is:

• A.  Dependency preserving and lossless.
• B.  Dependency preserving and lossy.
• C.  Neither dependency preserving nor lossless.
• D.  Not dependency preserving but lossless.

Answer 1

For dependency preserving all the FD's must be preserved

R1 (A,B): A->B ,

R2 (B,C): B->C,

R3 (D,E): D->E

therefore all preserved and is dependency preserving

For Lossless join: Ri U Rj U ..... U Rn = R and for any 2 Ri and Rj , (Ri intersection Rj) ->Ri or Rj

R1 U R2 U R3 = R     and

(R1 intersection R2) = {A,B,C} = R4

(R4 intersection R3) = {}

therefore is lossy.

So option is B. Dependency preserving and lossy