preliminaries 3.1. Fuzzy set and fuzzy logic The development of the theory of fuzzy sets can be attributed to Zadeh (1965). Nowadays, it has been a fundamental tool in artifi- cial intelligence with broad application in decision support (Jiang and Chen, 2005), expert system (Baraldi et al., 2009), pattern recognition (Mitra and Pal, 2005) etc. The concept of fuzzy set is a generalization of a regular crisp set. A fuzzy subset is defined in terms of a membership function which is a mapping from the universal set U to the interval [0,1]. Zadeh suggested the minimum operator for the intersection and the maximum operator for the union of two fuzzy sets. Basically, Fuzzy Logic is a many-valued logic that allows intermediate values to be defined between conventional two-valued logic, thus partial truth can be handled in reasoning with vagueness or uncertainty.