Fuzzy Functional Dependencies (FFDs) as Integrity Constraints
Since functional dependency (FD) is an important notion of nowadays database technology, its fuzzy extension has attracted a lot of attention, especially since the late 1980’s (Buckles and Petty, 1982; Prade and Testemale, 1983; Zemankova and Kandel, 1984; Raju and Majumdar, 1988; Kiss, 1990; Chen, Kerre and Vandenbulcke, 1991,1995; Dubois and Prade, 1992; Cubero and Vila, 1994). Consequently, different definitions of fuzzy functional dependencies (FFDs) emerged, resulting from the application of fuzzy logic to the conventional FD in various manners, and to different extents. Usually, each of such definitions of fuzzy functional dependencies is associated with its own framework of fuzzy database model (fuzzy data representation), therefore is normally relevant merely within the framework, although there always exist basic properties and essential characteristics that need or are desirable to possess.
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