Golfer22 (8/11/2013)
Here is the definition of 3NF:"A relation R is in 3NF if and only if (i) it is in 2NF and (ii) whenever X is a set of attributes of R and A is a non-key attribute of R that is not in X, the value of A can be determined from the values of X only if X includes a candidate key."
If a relation is in 2NF by the definition in the first response to my original post, how could it not be in 3NF?
I think you are probably having trouble with Codd's phrase "fully dependent on"; what it means is "determined by the whole of but not by any proper subset of".
The easiest way to see the difference between 2nd and 3rd normal form is to take your 3NF definition above and insert the word "prime" before "attributes", which transforms it into a definition of 2NF.
2NF says: a non-prime attribute can't be determined from a proper subset of a candidate key. 3NF says in addition that it can't be determined from anything but a candidate key.
Tom