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چکیده
ln a fuzzy relational database where a relation is atuzzy sel of tuples and ill-known data are represented by possibility distributions, nested fuzzy queries can be expressed in lhe Fuzzy SQL language, as defined in [25], [23]. Although it provides a very convenient way for users to express complex queries, a nested fuzzy query may be very inefficient to process with the naive evaluation method based on its semantics. ln conventional databases, nested queries are unnested to improve the etficiency of their evaluation. ln this paper, we extend the unnesting techniques to process several types of nested fuzzy queries. An extended merge-join is used to evaluate the unnested fuzzy queries. As shown by both theoretical analysis and experimental results, the unnesting techniques with the extended merge-join significantly improve the performance of evaluating nested fuzzy queries. lndex Terms-Fuzzy database, luzzy SQL, nested luzzy query, query optimization, query transformation, possibility distribution, performance evaluation.fuzzy equijoin.
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تاریخ انتشار 2011