SOME APPROACHES FOR PROCESSING SQLF NESTED QUERIES

This article deals with query processing techniques for the SQLf langu age which is an extended version of SQL supporting imprecise queries i nterpreted in the framework of fuzzy sets. SQLf, as well as SQL, allow s for the use of nested queries, in which a (fuzzy) condition involved in a select block, calls on another select block (the nested one). Tw o types of processing strategies for nested queries are discussed. The first one tends to take advantage of existing database management sys tems (DBMS) to process fuzzy queries thanks to an additional layer whi ch is in charge of translating the initial query into a Boolean one. I n this perspective, the performances obtained depend strongly on the e fficiency of the underlying DBMS. The other strategy is slightly diffe rent and it is situated in the context of the design of systems involv ing specific algorithms for processing fuzzy queries. In this article, the focus is put on algorithms related to the generic nesting constru ct ''exists.'' (C) 1996 John Wiley & Sons, Inc.