Home Forums Database Design Design Ideas and Questions Second normal form or third normal form? RE: Second normal form or third normal form?

  • August 12, 2013 at 2:30 am

    #1640476

    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?

    Because the fact that non-key attribute A is fully dependent on keys doesn't exclude the possibility that it may have other non-key detereminants as well. 2NF doesn't exclude the possibility of those non-key determinants. 3NF does.