NDLI: Semantic query optimization for tree and chain queries

Content Provider	IEEE Xplore Digital Library
Author	Wei Sun Yu, C.T.
Copyright Year	1989
Abstract	Semantic query optimization, or knowledge-based query optimization, has received increasing interest in recent years. The authors provide an effective and systematic approach to optimizing queries by appropriately choosing semantically equivalent transformations. Basically, there are two different types of transformations: transformations by eliminating unnecessary joins, and transformations by adding/eliminating redundant beneficial/nonbeneficial selection operations (restrictions). A necessary and sufficient condition to eliminate a single unnecessary join is provided. We prove that it is /spl Nscr//spl Pscr/-/spl Cscr/omplete to eliminate as many unnecessary joins as possible for various types of acyclic queries with the exception of the closure chain queries whose query graphs are chains and all equi-join attributes are distinct. An algorithm is provided to minimize the number of joins in tree queries. This algorithm has an important property that, when applied to a closure chain query, it will yield an optimal solution with the time complexity O(n*m), where n is the number of relations referenced in the chain query, and m is the time complexity of a restriction closure computation.<>
Sponsorship	IEEE IEEE Comput. Soc. Tech. Committee on Data Eng IEEE Computer Society
Starting Page	136
Ending Page	151
Page Count	16
File Size	1769422
File Format	PDF
ISSN	10414347
Volume Number	6
Issue Number	1
Language	English
Publisher	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Publisher Date	1994-02-01
Publisher Place	U.S.A.
Access Restriction	One Nation One Subscription (ONOS)
Rights Holder	Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subject Keyword	Query processing Databases Sun Qualifications Tree graphs Marine technology Sufficient conditions Oceans Councils Computer science
Content Type	Text
Resource Type	Article
Subject	Information Systems Computational Theory and Mathematics Computer Science Applications

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