How to determine a partial functional dependency when checking for second normal form ?

Question

What is the best and the most accurate way to check if a given functional dependency is partial on the set of FDs given. Earlier, I used to follow {part of CK -> non prime attribute} as the rule, but in several of the questions I find that this rule alone is not sufficient. Can someone give a fully working technique to solve for such cases ?

For instance, I was reading a question on stack overflow, where in a relation r(ABCD), the following FDs hold- AB->CD, AB->C and A->C.

As the CK is AB,the partial FDs should be A->C . But one of thetop users has commented that the dependency Ab->C is partial and A->C is full. ?? :/

Question link for reference (http://stackoverflow.com/questions/25747802/partial-dependencydatabases ) see answer by 'Mike Sherrill 'Cat Recall''

Answer 1

A functional dependency X → Y is a full functional dependency if removal of any attribute A from X means that the dependency does not hold any more; that is, for any attribute A ε X, (X – {A}) does not functionally determine Y.

A functional dependency X → Y is a partial dependency if some attribute A ε X can be removed from X and the dependency still holds; 

Here if we remove B from AB→C

We get A→C (as A→C holds bcz it is in fd already)

If we remove B From there  AB→C can't hold any more C fully depends on A.

So C partially depends on AB and  AB→C is partial fd

Read answer of philipxy or his replies ovr the comment carefully.

Answer 2

Fd on the right hand side of partial dependency should be proper subset of any candidate key. So AB is not proper subset of of CK. Hence there is only one partial Dependency.

Comments

Right!

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@JEET please have a look at this definition

 

Partial dependency means that a non prime attribute is functionally dependent on part of a candidate key. (A non prime attribute is an attribute that's not part of any candidate key.)

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Yeah, I know this. :D

Between thanks.