Difference between revisions of "Normalization"
From Wiki Notes @ WuJiewen.com, by Jiewen Wu
m (New page: ==Functional Dependency (FD)== A FD on a relation scheme R is a constraint X->Y, where X and Y are sets of attributes. For a pair of tuple t and s, they satisfies the above FD if they agre...) |
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==Functional Dependency (FD)== | ==Functional Dependency (FD)== | ||
− | A FD on a relation scheme R is a constraint X->Y, where X and Y are sets of attributes. For a pair of tuple t and s, they satisfies the above FD if they agree on all attributes in Y | + | A FD, an integrity constraint, on a relation scheme R is a constraint X->Y, where X and Y are sets of attributes. For a pair of tuple t and s, they satisfies the above FD if they agree on all attributes in Y whenever they agree on all attributes in X. |
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+ | Some properties of FDs. | ||
[[Category:Database Topics]] | [[Category:Database Topics]] | ||
+ | * Trivial (Reflexive) FDs: X->Y if Y is a subset of X. | ||
+ | * Augmentation: if X->Y then XZ->YZ | ||
+ | * Transitivity: if X->Y and Y->Z, then X->Z. | ||
+ | * Union: if X->Y and X->Z, then X->YZ. | ||
+ | * Decomposition: if X->YZ, then X->Y and X->Z. |
Revision as of 13:06, 5 August 2010
Functional Dependency (FD)
A FD, an integrity constraint, on a relation scheme R is a constraint X->Y, where X and Y are sets of attributes. For a pair of tuple t and s, they satisfies the above FD if they agree on all attributes in Y whenever they agree on all attributes in X.
Some properties of FDs.
- Trivial (Reflexive) FDs: X->Y if Y is a subset of X.
- Augmentation: if X->Y then XZ->YZ
- Transitivity: if X->Y and Y->Z, then X->Z.
- Union: if X->Y and X->Z, then X->YZ.
- Decomposition: if X->YZ, then X->Y and X->Z.