2011 by Taylor & Francis Group, LLC. In a broader scope, a transformation in mathematics can broadly be defined as the operation which takes its input and represents it in a different form. Such a definition immediately implies preserving the essential characteristics of the input through several conservation rules or laws. In order to outline the complete input-output relationship in an abstract transformation, the input and output of the transformation should be characterized as well. Therefore, mathematically speaking, a transformation can be viewed as a special function (or a correspondence) whose input and output can be a single value or another function. In this context, signals are considered to be both input and output functions of the transformation of interest.