25 lines
727 B
Plaintext
25 lines
727 B
Plaintext
Types of conflicts:
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- rw
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- wr
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- ww
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Conflicts in timestamping are directed: the second of the transactions is said to conflict with the first, not vice-versa.
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When a cycle is formed in the transaction graph, the transaction is killed.
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BCNF: all determinants (left-hand sides of FDs) are candidate keys
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AB -> C
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C -> B
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C+ = {C, B} != R
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Minimal cover set:
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1. RHS should be singletons
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i.e. X -> YZ becomes X->Y X->Z
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2. minimal LHS
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i.e XYZ -> W and YZ -> W then XYZ->W is redundant and should just be replaced with YZ->W
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3. No redundant FDs
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in general, use an example of your own rather than given
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- "as far as he knows", it's all examples from your own imagination"
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