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Outline

Non if-then fuzzy models

2000, Studies in Fuzziness and Soft Computing

https://doi.org/10.1007/978-3-7908-1850-5_7

Abstract

In Chapter 1 we adopted Definition 1 stating that a fuzzy classifier is any classifier which uses fuzzy sets either during its training or during its operation. So, fuzzy classifier modeling stretches beyond fuzzy if-then designs discussed in the previous two chapters. This chapter presents nonif-then fuzzy models. These models can be grouped in different ways (see [39,81, 115, 118, 273, 320]). However, the boundaries between these groups are not sharp because many of the classification schemes can be assigned to more than one group (see, e.g., [232] where the authors use multiple rulebased prototypes and call their method a knowledge-oriented fuzzy k-nearest neighbor classifier). 7.1 Early ideas The first ideas about using fuzzy sets in classification emerged soon after fuzzy sets were introduced by Zadeh in 1965. The seminal paper by Bellman, Kalaba and Zadeh [26] defines a fuzzy classification environment where the problem is to design a classifier producing soft labels. They call abstraction the process of finding a set of discriminant functions gi : !Rn-+ [0,1], i = 1, ... ,e, from the labeled data set Z. This corresponds to training the classifier. Calculating a soft labeI for a given x E !R n , not in Z, is called generalization. 7.1.1 Fuzzy and probabilistic models Various relationships between fuzziness and probability have been explored. Combinations of fuzzy and probabilistic types of uncertainty have been sought at a rather theoretical level. Examples of this are fuzzy probability spaces [160], fuzzy Bayes classification (fuzzy-statistical and statistical-fuzzy models) [86, 236], fuzzy-Bayes decision making [320], etc. Replacing the probability density functions (p.dJ's) in the classical statistical pattern recognition model (Chapter 2) by membership functions has appealed to many authors as a logical substitute. This choice has been continuously disputed ever since it emerged. The idea of substitution has given rise to the possibilistic models for classification where possibilistic distributions are constructed