0 votes 0 votes R (A, B, C ,D ,E ) F={ A->B, BC-> D, D->BC, B->E, B->A } Check whether BD is C.Key or S.key . Also find the candidate key. dhairya asked Jun 18, 2016 dhairya 2.0k views answer comment Share Follow See all 0 reply Please log in or register to add a comment.
Best answer 5 votes 5 votes BD+ ={BDEAC} D+={DBCEA} Since D alone is Ck implies BD is super key Candidate Keys D+={ABCDE} By replacing D with BC BC+={ABCDE} By replacing B with A AC+={ABCDE} These are candidate keys D,AC,BC shivanisrivarshini answered Jun 18, 2016 • edited Jun 18, 2016 by LeenSharma shivanisrivarshini comment Share Follow See all 14 Comments See all 14 14 Comments reply Show 11 previous comments dhairya commented Jun 19, 2016 reply Follow Share ohh..okk...f9.. So every time when we will have more than 2 C.Key.. we will subtract all the possible combination of repetetion then add 1 S.K which is the mixture of all the attributes. EX-- R (A,B,C,D,E,F) Suppose AC, DE, BF are the Candidate keys.. then , SK= n(AC)+ n(DE) +n(BF) - n( AC ∩ DE ) - n( DE ∩ BF ) - n( AC ∩ BF ) + n( ABCDEF ) Am i right...?? 0 votes 0 votes LeenSharma commented Jun 19, 2016 reply Follow Share yes,Right. It's kind of Set theory Problem. 0 votes 0 votes dhairya commented Jun 19, 2016 reply Follow Share okk...thank u @LeenSharma .. :D :D 1 votes 1 votes Please log in or register to add a comment.
6 votes 6 votes Ck with single attribute : D+ =ABCDE // This is the only Ck with single attribute Ck with 2 attributes : AC+ =ABCDE BC+ =ABCDE // These are the only 2 Ck's with 2 attributes There is no Ck with 3 attributes : There is no Ck with 4 attributes : Now your question whether BD is a Ck Or Sk you can see that D is already proven to be Ck So BD will be a Sk Here not a Ck . shekhar chauhan answered Jun 18, 2016 • edited Jun 18, 2016 by shekhar chauhan shekhar chauhan comment Share Follow See all 3 Comments See all 3 3 Comments reply shivanisrivarshini commented Jun 18, 2016 reply Follow Share CEA ,CEB are super keys right 0 votes 0 votes Tauhin Gangwar commented Jun 18, 2016 reply Follow Share chauhan when...AC is candidate key how CEA can b candidate key 0 votes 0 votes shekhar chauhan commented Jun 18, 2016 reply Follow Share my mistake sorry 1 votes 1 votes Please log in or register to add a comment.