New answers tagged databases
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Second normal form means that each non prime attribute must not depend on a proper subset of a candidate key.
In your example, assuming that the given FDs are a cover of the FDs of the relation, you have two candidate keys, ABC and ABD. Moreover, the attribute E depends on BC, which is a proper subset of the candidate key ABC (you can verify this by ...
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Databases have some issues that "mere mortal" data storage doesn't concern itself with, such as transaction safety and disk failure.
Here are a few classic papers on the topic:
Astrahan et al (1976), System R: A Relational Approach to Data Base Management, ACM TOMS 1:2, pp 97-137.
Stonebreaker et al (1976), The Design and Implementation of INGRES, ...
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X -> Y non-trivial means that X does not include Y. Since Y is a prime attribute, we know that there is at least a candidate key that include it. Let's call this key K1.
Now we have two cases: either X is a superkey, or not.
If X is a superkey, then it contains at least a candidate key K. We can easily convince that K ≠ K1, since it differ from K1 by at ...
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