Supervised versus unsupervised learning

It's not hard to see from looking at the popular press that one of the hottest areas in artificial intelligence today is machine learning. Machine learning is commonly classified into supervised and unsupervised learning. Other classifications exist, but we'll discuss those later.

Let's get some intuitive understanding about supervised learning versus unsupervised learning before we give a more formal definition. Assume you have a set of portraits of people. The people in this set are a very diverse group of men and women and you have all kinds of nationalities, ages, body weights, and so on. Initially, you put the dataset through an unsupervised learning algorithm. In this case, without any a priori knowledge, the unsupervised algorithm will start classifying these photographs depending on some feature that it recognizes as similar. For example, on its own, it might start recognizing that men and women are different, and it...