Some approaches for processing SQLf nested queries
Patrick Bosc · International Journal of Intelligent Systems · 1998
This article deals with query processing techniques for the SQLf language which is an extended version of SQL supporting imprecise queries interpreted in the framework of fuzzy sets. SQLf, as well as SQL, allows for the use of nested queries, in which a (fuzzy) condition involved in a select block, calls on another select block (the nested one). Two types of processing strategies for nested queries are discussed. The first one tends to take advantage of existing database management systems (DBMS) to process fuzzy queries thanks to an additional layer which is in charge of translating the initial query into a Boolean one. In this perspective, the performances obtained depend strongly on the efficiency of the underlying DBMS. The other strategy is slightly different and it is situated in the context of the design of systems involving specific algorithms for processing fuzzy queries. In this article, the focus is put on algorithms related to the generic nesting construct “exists.” © 1996 John Wiley & Sons, Inc.