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What is Functional Dependency in database?

What is Functional Dependency in database?

A Functional dependency is denoted by X----> Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.

A functional dependency ,say X->Y means X determines Y or Y is functionally dependent on X(X is a candidate key).It is a constraint from 2 set of attributes from the database.

[b]for example,for 2 tuples t1 and t2 in R if t1[X]=t2[X] ,  then [/b]



[b]                                                                        t1[Y]=t2[Y].[/b]