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+4 votes

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)
it means in multivalue dependency we don't care about functional dependency?
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 .

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

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

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