| 摘要 |
PROBLEM TO BE SOLVED: To provide a means which optimizes database retrieval from a multi- database system. SOLUTION: A database inquiry tree is reconstructed by performing an optimizing process in two steps for optimizing inquiry/response time. In the first optimizing step, a linkage tree which has a route inquiry node, a plurality of low-order inquiry nodes, and a plurality of table nodes each of which has left- and right-side slave sub-trees and is deep on the left side is generated. Then the response time of the route and low-order nodes and the access/response time to each table node are estimated. In the second optimizing step, the linkage tree is transformed into a balanced linkage tree by using the response time data so that the costs of the left-side slave sub-trees can substantially become equal to those of the right-side slave sub-trees. Finally, data are fetched from a related data base in response to the inquiry corresponding to the balanced inquiry tree.
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