Question

The following functional dependency hold for relations R (A,B,C) and S(B,D,E):FD FOR BOTH THE TABLES B -> A, A -> C  The relation R contains 200 tuples and the relation s contains 100 tuples. What is the maximum 4 number of tuples possible in natural join R|><|S?

Answer 1

B is  primary key fro R as B->A B->C  

B is foreign key for S

Max tuples in natural join of R and S  will be min(200,100)=100

(As B is primary key all B values in relation R are distinct Now when we join R and S it may happen that any one of 200 value may map to all 100 values or say 100 values from 200 may map to 100 values of S These are just to cases)

Comments

@ pranay I think its typo ...it is just asking for max no of tuples in join..that 4 has no meaning with respect to question

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some one correct this

B is  primary key fro R as B->A B->C  
B is foreign key for S

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we need to assume "B is foreign key for S" right ?

other wise answer could be different right ?

Answer 2

B is the primary key. since A is functionally dependent on B and C is f.d on A so you can derive the value of A and C from B only .

as natural join is the equijoin on the common attribute B, it will have a maximum of 100 tuples