CHAPTER Input: Concepts, Instances, and Attributes 2 Before delving into the question of how machine learning schemes operate, we begin by looking at the different forms the input might take and, in Chapter 3, the different kinds of output that might be produced. With any software system, understanding what the inputs and outputs are is far more important than knowing what goes on in between, and machine learning is no exception. The input takes the form of concepts, instances, and attributes. We call the thing that is to be learned a concept description. The idea of a concept, like the very idea of learning in the first place, is hard to pin down precisely, and we won't spend time philosophizing about just what it is and isn't. In a sense, what we are trying to find--the result of the learning process--is a description of the concept that is intel-