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I understood all the three normal forms which comes before BCNF but when it comes to the BCNF i am finding it extremely confusing and difficult and over the net also i found no good tutorial on it. Can any one explain what to do in order to make relation in BCNF form precisely ?

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    The wikipedia article on it is actually pretty clear. What SPECIFICALLY are you having issues with? This is not the place to ask extremely general questions about tutorials and such.
    – JNK
    Nov 22, 2011 at 14:56
  • I read the wiki article on BCNF but the example given there are not clear and i am also having questions in their examples. The examples i am facing frequently is (AB->C) and (C->B). Then it is transitive dependency which will be removed in 3NF. so what to do in BCNF ? I am not getting any continuous example where all the normalization forms are derived from the one case study. That's the reason i posted question here.
    – Ankur Trapasiya
    Nov 22, 2011 at 18:22
  • As mentioned in the wiki article, your example CAN'T be put into BCNF. It's not universally applicable.
    – JNK
    Nov 22, 2011 at 18:23
  • @JNK: I am not getting it.
    – Ankur Trapasiya
    Nov 22, 2011 at 18:27

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BCNF fixes a minor flaw in 3NF

2NF and 3NF talk about non-key attributes:

  • 2NF requires non-key atributes depend only on the whole key
  • 3NF requires non-key attributes don't depend on each other

BCNF tidies up intra-key attributes. It requires (in 3 different ways):

  • you don't have 2 candidate keys within the one key generated by 3NF
  • key attributes don't depend on other key attributes
  • no overlapping candidate keys (that is, the 3NF key is a super key of one or more other candidate keys)

As the various tutorials say, you probably don't need it..

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  • Thanks for reply. I read about it and i came to conclusion that a relation is in BCNF iff "every determinant is the candidate key". Now i am not getting your third point which is overlapping candidate keys. What is it ?
    – Ankur Trapasiya
    Nov 22, 2011 at 18:10
  • "As the various tutorials say, you probably don't need it" -- I've seen tutorials take the opposite view i.e. if BCNF fixes 3NF (your words) then we no longer need 3NF.
    – onedaywhen
    Apr 16, 2012 at 10:31

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