### Thread: Non trivial functional dependencies

1. #### Non trivial functional dependencies

Hi

Im not sure if this is the correct place to post this but it is to do with database management slightly.

I am basically having a problem with a possible exam question for my degree exam module database systems.

I have searched google, wikipedia, my lecture notes and some paper i found from toronto and am still having trouble understanding a non trivial functional dependency!

I know that a functional dependency is when:

A -> B (A determines B)
B -/> A (B is determined by A) -/> meant to be does not determine!

Ive read my notes and it says that a functional dependency is trivial if satisfied by all tuples. However I dont really understand this.

My exam question is as follows:

Give a full explanation of the terms functional dependency (FD) and non-trivial FD.

List all the non-trivial functional dependencies (FDs) satisified in the following table

Code:
```   A       B       C
a1     b1      c1
a1     b1      c2
a2     b1      c1
a2     b1      c3```
Please if someone knows could they tell me as Ive been trawling the net for an hour and a half on this question and still havent worked it out. Please if possible do not link me to more pages Im sure its a lot simpler than im making it out to be!

Billabang
2. Sadly didnt get a lot of response in the forum. Must admit that doesnt happen often though

Ive found out that non trivial functional dependencies are anthing that is NOT:

A -> A (where an attribute determines itself)
A -> B where B is contained in or is a subset of A

As these are all trivial and therefore NOT useful.

The non trivial FDs from that table are as follows:

a1 -> b1
a2 -> b1
c1 -> b1
c2 -> b2

Hope this helps anyone that gets the same problem