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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 '11 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 '11 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 '11 at 18:23
    
@JNK: I am not getting it. –  ankur.trapasiya Nov 22 '11 at 18:27

1 Answer 1

up vote 2 down vote accepted

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 '11 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 '12 at 10:31

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