If I have: R(NPQSTVWXYZ) with functional dependencies: f=(y->sz, tw -> n, ntwx -

Question

If I have:

R(NPQSTVWXYZ)

with functional dependencies:

f=(y->sz, tw -> n, ntwx -> qy, n->tw, x->qy, v->sz, q->pv)

and sub-relations:

R1(PQV) R2(NTW) R3(SVYZ) and R4(QXY)


How would I find the functional dependencies that apply to each sub relation?

If I have:

R(NPQSTVWXYZ)

with functional dependencies:

f=(y->sz, tw -> n, ntwx -> qy, n->tw, x->qy, v->sz, q->pv)

and sub-relations:

R1(PQV) R2(NTW) R3(SVYZ) and R4(QXY)


How would I find the functional dependencies that apply to each sub relation?

Explanation / Answer

HI,

To search for functional dependencies in each relation, check the list of functional depedencies that contain two or more of the relation's attributes only.

Now,

fd1 : y->sz

fd2 : tw -> n

fd3 : ntwx -> qy

fd4: n->tw

fd5: x->qy

fd6: v->sz

fd7: q->pv

for instance, take R1.

R1 has 3 attributes P,Q,V.

Check Fds    f1 to f7.

You can see that only f7 has 2 or more attributes matching R1.

So

fd7: q->pv applies to R1

Similarly,

For R2 attributes : NTW  

fd2: tw->n

fd4 n->tw

we dont include fd3 because it is a trivial functional dependency, i.e , since fd5 states x->qy , fd3 is not needed in F.

For R3 attributes : SVYZ

fd1: y->sz

fd6: v->sz

For R4 attributes : QXY

fd5 : x->qy

Hope it helps :)

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