4 votes 4 votes A 3NF table which does not have multiple overlapping candidate keys is said to be in a)1NF b)2NF c)4NF d)BCNF Databases databases database-normalization + – A_i_$_h asked Sep 9, 2017 • retagged May 27, 2021 by Shiva Sagar Rao A_i_$_h 2.3k views answer comment Share Follow See all 14 Comments See all 14 14 Comments reply Shubhanshu commented Sep 9, 2017 reply Follow Share 2NF?? 0 votes 0 votes A_i_$_h commented Sep 9, 2017 reply Follow Share the answer given is BCNF 0 votes 0 votes Shubhanshu commented Sep 9, 2017 reply Follow Share I have counter case R(ABCD) A -> BC, B- AC, C->D keys - {A} and {B} not overlaping and in 2NF. 0 votes 0 votes A_i_$_h commented Sep 9, 2017 reply Follow Share a 3NF table.....its not in 3NF right?? because of C->D 0 votes 0 votes Shubhanshu commented Sep 9, 2017 reply Follow Share Yes it is not in 3 NF because C->D. 0 votes 0 votes A_i_$_h commented Sep 9, 2017 reply Follow Share the question is ..... a 3NF table which does not have overlapping... so i guess it should be BCNF whats this 4NF by the way? 0 votes 0 votes stanchion commented Nov 3, 2017 reply Follow Share I have counter case. R(ABCDEF) AB -> CDEF, CD -> ABEF, E->D KEY={ AB, CD} - NON OVERLAPPING C K Also table R is in 3NF ( don't get confused with FD: E->D as it is from NON_KEY -> KEY_ATTRIB) So, this table R is in 1NF, 2NF 3NF (AT MAX) , (not in BCNF) Answer option B 0 votes 0 votes saxena0612 commented Nov 3, 2017 reply Follow Share @stanchion AB -> CDEF ==> AB->E E=D Table in 3nf? 0 votes 0 votes Shubhanshu commented Nov 3, 2017 reply Follow Share @stanchion the Relation given in your comment is in 3nf not in 2nf, and its CK are {AB, CD, CE } because of E->D, E is no longer non-prime attribute since it is determining prime attribute, and the FD is satisfying 3NF. And relation not has non overlapped CK. 0 votes 0 votes Anu007 commented Nov 3, 2017 reply Follow Share the Relation given in your comment is in 3nf not in 2nf, is it possible??? To be in 3NF primary condition is it is in 2NF. 1 votes 1 votes stanchion commented Nov 3, 2017 reply Follow Share Yes. Thanks for your correction. I made a mistake in my earlier example. 0 votes 0 votes stanchion commented Nov 3, 2017 i reshown by stanchion Nov 4, 2017 reply Follow Share Ans will be BCNF Given condition: a relation is already in 3NF and multiple CKs exist and they must be non overlapping. Now, lets analyze: If a table is in 3NF then all the FDs X->Y must be either case (1) : X is SK (satisfies BCNF property) or case (2) : Y is Prime_Attrib (we have to analyze this case where X- non_key, Y- prime_Attribute.) Now, If such case exist i.e. Non_key -> Prime_Attrib then there must be overlapping CK (which violates given condition). So if a table is in 3NF and multiple non overlapping CKs are present then case (2) i.e Non_key->Prime_Attrib. It means table becomes BCNF. Lets understand this point by an example: R( ABCDEF) - 3NF and FDs are: { ABC->DEF, D->ABCEF , E->B } // I have deliberately put FD "E->B" to avoid BCNF form. So if i do so then my CK becomes overlapping. ie CK= { D, ABC, ACE} - violates initial condition. So FDs like E->B can't exist in 3NF, multiple non overlapping CKs. So Correct Ans- Option D (BCNF) 4 votes 4 votes Sanjay Moharana commented Jan 8, 2018 reply Follow Share @stanchion Nice Explanation 1 votes 1 votes hacker16 commented Jan 13, 2018 reply Follow Share i didn't get how can we inference BCNF from, "A 3NF table which does not have multiple overlapping candidate keys is said to be in" . someone, please explain it. 0 votes 0 votes Please log in or register to add a comment.