Tom.Thomson (7/28/2011)

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James Goodwin (7/28/2011)

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The difference between 2NF and 3NF is that 2NF does not permit any non-prime attribute to have a dependency on something which is a proper subset of a candidate key, while in 3NF a non-prime attribute may not depend on anything which is not a superkey

My confusion is that the original table in the example is, then, not in 2NF because the phone number depends on something (Group) that is not the whole key, or in fact, even part of the key. So it seems that you took a table from 1NF to 2NF which was then trivially in 3NF (in the sense that no extra work was required to get it into 3NF).

What I would like to see is a table that is in 2NF converted into 3NF.

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JimFive

Ah, a confusion about 2NF. You hit the crucial point when you said "or [not] in fact, even part of [the key]", because that is of course allowed by 2NF. There's nothing in 2NF to stop an attribute being dependent on some set of attributes that includes something that isn't part of a key. The rule is that if a non-prime attribute is dependent on something that is a subset of a key that subset must be the whole key. Or putting it another way, the whole key is not the only thing it can be dependent on, the rule is simply that it must never be dependent on a partial key. So the original table inthe 3NF article is indeed in 2NF.