ch5-p2 - Distributed Database Systems Chapter 5 f

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fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff ffffffffffffffffff000000000000000000000000000000000000000000000000000000000000 fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff Distributed Database Systems Chapter 5 A set of simple predicates Pr is minimal if all of its predicates are relevant. COM_MIN Algorithm 12
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Distributed Database Systems Chapter 5 Algorithm COM_MIN Input: R: relation; r P :set of simple predicates Output : r ' P :set of simple predicates with properties of completeness and minimanity Declare F: set of minterm fragments Begin Find a r i P p such that i p partitions R by Rule 1 r r p ' P i r r p p P - i f F { i f is the minterm fragment of i p } do begin find a r j P p s.t. j p partitions some k f of ' P r according to Rule 1 j r r p ' P ' P j r r p P P - j f F F if ' P p r k 5 which is nonrelevant then begin k r r p ' P ' P - k f F F - end-if end-begin until is ' P r complete End.{COM_MIN} The second step To derive the set of minterm predicates -- trivial. 13
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Distributed Database Systems Chapter 5 Minterm predicates are exponential on the number of simple predicates. The third step To eliminate meaningless minterm predicates by identifying those that contradict to a set of implications I . Example ' P r ={att=value_1,att=value_2} domain(att)={value_1,value_2} I: ) _ value att ( ) _ value att ( 2 1 = ¬ = ) _ value att ( ) _ value att ( 2 1 = = ¬ Four minterm predicates generated from ' P r ) _ value att ( ) _ value att ( m : 1 2 1 = = ) _ value att ( ) _ value att ( m : 2 2 1 = ¬ = ) _ value att ( ) _ value att ( m : 2 1 3 = = ¬ ) _ value att ( ) _ value att ( m : 2 1 4 = ¬ = ¬ 1
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ch5-p2 - Distributed Database Systems Chapter 5 f

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