Chapter 6 Normalization
Chapter 6 Normalization
Chapter 6 Normalization
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What is missing<br />
Although the above decomposition is lossless,<br />
something is wrong: the following FD is homeless.<br />
ClientId,OfficeId → AccountNumber<br />
Notice that the FD AccountNumber → OfficeId<br />
can be checked locally via one of the schemas,<br />
verification of the missing FD has to be done<br />
via a join of two tables.<br />
Thus, this decomposition leads to an increased<br />
cost of maintaining an integrity constraint that<br />
corresponding to the above FD.<br />
In such a case, we say that the decomposition,<br />
although lossless, does not preserve the<br />
dependency in the original schema.<br />
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