relational database and functional dependencies
Can one infer the primary key from a group of functional dependencies?
Consider the relation R(A, B, C, D, E, G, H) and the FD set F={AB¿C, AC¿B, AD¿E,
B¿D, BC¿A, E¿G}
the question then asks if R is in 3NF and BCNF. I can answer the question in regards to a primary key, but one is not given. so this begs the question, can a primary key be derived from FDs?
Consider the relation R(A, B, C, D, E, G, H) and the FD set F={AB¿C, AC¿B, AD¿E,
B¿D, BC¿A, E¿G}
the question then asks if R is in 3NF and BCNF. I can answer the question in regards to a primary key, but one is not given. so this begs the question, can a primary key be derived from FDs?
hi,
when I understand you and you're problem description is correct, then the answer is simple: the PK contains only the attributes without dependency - which is obviously and easy to spot.
mfG
--> stefan <--
p.s.: I hope it's not a kind of homework question...
when I understand you and you're problem description is correct, then the answer is simple: the PK contains only the attributes without dependency - which is obviously and easy to spot.
mfG
--> stefan <--
p.s.: I hope it's not a kind of homework question...
ASKER
I suppose if it was obvious I would not be asking. They all have dependencies except for H and it would seem hard to accept it is the primary key.
So what about G? E depends on G, but G has no dependency. So, (G, H) should be a candidate key.
ASKER
ok, I see that. is that the only candidate key?
ASKER
but I thought e->g meant that g is dependent on e, not e is dependent on g
btw, not that I read it wrong, does AB->C means C depends on AB or AB depends on C?
ASKER
AB defines or implies C
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ASKER
He deserves points for being only person whom took the time to assist me.
ASKER