These activities can be very complex and, even worse,are rarely addressed in isolation. They are invariably interrelated.The rest of this section is devoted to explaining
where the complexity of classifier design comes from so that the need for a system which automates the classifier design process is clearly justified.
For practical applications, data pre-processing is often a necessary step in the development of solution. In the simplest case, pre-processing may take the form of a linear rescaling of the input variables so that they have similar values regardless of the units in which each of these is expressed. More complex pre-processing may involve
reduction of the dimensionality of the input data.