1

Given the following set of function dependencies

A -> B 
B -> C
B -/> A     (B doesn't functionally determine A)

if A->C exist, it is a transitive dependency

What if we are given the following 2 situations, are they transitive dependency too?

First situation

A -> B
B -> C
C -> D
B -/> A
C -/> B

is A->D a transitive dependency?

Second situation

A -> B
B -> C
C -> D
B -/> A
C -> B

is A->D a transitive dependency?

Steve Ng
  • 1,189
  • 1
  • 13
  • 35

1 Answers1

1

The example is trivial. You don't even need to clarify when something is NOT a TD. It is assumed that nothing is a TD but the TDs you explicitly define. So the first step is to remove the redundancy of all 

X -/> Y

Now, given:

A -> B
B -> C
C -> D

The following are transitive dependencies:

A -> C
A -> D
B -> D

Adding any other dependencies won't change the current transitive dependencies

Mosty Mostacho
  • 42,742
  • 16
  • 96
  • 123
  • Thanks! That's for the first situation, what about the second situation? is A->D a transitive dependency too? – Steve Ng Oct 13 '13 at 02:25
  • Actually, that covers both situations, because they happen to be the same. As I mentioned in the last comment, `adding any other dependencies (such as C -> B) won't change the current TDs`. – Mosty Mostacho Oct 13 '13 at 04:46