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It has six specific rule to be precise.....

1)Use impotence of selection and projection to generate appropriate selections and projections for each operand relation.

2)Push selections and projections down in the tree as far as possible.

3)push selections down to the leaves of the tree, and then apply them using the algebra of qualified relations; substitute the selection result with the empty relation if the qualification of the result is contradictory.

4)Use the algebra of qualified relations to evaluate the qualification of operands of joins; substitute the subtree, including the join and its operands, with the empty relation if the qualification of the result of join is contradictory.

5)In order to distribute joins which appear in the global query, unions must be pushed up,beyond the joins that we want to distribute.

6)In order to distribute grouping and aggregate function evaluations appearing in a global query,unions must be pushed up,beyond the corresponding group-by operation.

refer some books of distributed database design or contact me for further explanations...

Avik Chatterjee

Lecturer

Techno India Hooghly

9038223317

cavik81@gmail.com

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14y ago

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