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Every time the attribute A appears, it is matched with the same value of attribute B but not the same value of attribute C. Which of the following is true?

  1. A -> (B,C)      
  2. A -> B, A ->> C      
  3. A -> B, C ->> A        
  4. A ->> B, B -> C
asked in Databases by Active (3.3k points) | 2.5k views

1 Answer

+10 votes
Best answer
the option b is correct . there is just a small definition of multivalue dependencies which . if a->> c is a dependency it means for a ,c has more than one value.

here it is saying whenever a appears b has same value which is true in case of functional dependency . if a->b exist for every a if repeats there should be same b . so a-.b exist here and it is clearly saying c is not same which means for same a it contains multipule value of c. so answer is b .
why not c ??

just consider the case
a is 1

and for c

A       C

1       3

1        4

now u can see that for a we have multipule value of c but c does not have multiple values for a . so we cannot say c->>a . but we can say a->>c. and question is saying c can take different value not a .
answered by Boss (15.9k points)
0
it means in multivalue dependency we don't care about functional dependency?
0
no basically the whole multi value functional dependency thing is lot more tricky. but reading it all and then just getting confussed is worthless. what i have taught is just a technique that is sufficient to answer every multivalue dependency question in gate. every function dependency is a multivalue dependency .
0

every function dependency is a multivalue dependency  but reverse may not be true?

0
yes
0
okey.
0
i did not get ...y c should not be answer..? plz explain  y not  c ????


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