e -C H A P T E R e-Chapter 6 Similarity-Based Methods “It’s a manohorse”, exclaimed the confident little 5 year old boy. We call it the Centaur out of habit, but who can fault the kid’s intuition? The 5 year old has never seen this thing before now, yet he came up with a reasonable classification for the beast. He is us- ing the simplest method of learning that we know of – similarity – and yet it’s effective: the child searches through his history for similar objects (in this case a man and a horse) and builds a classification based on these similar objects. The method is simple and intuitive, yet when we get into the details, several issues need to be addressed in order to arrive at a technique that is quantitative and fit for a computer. The goal of this chapter is to build exactly such a quantitative framework for similarity based learning. 6.1 Similarity The ‘manohorse’ is interesting because it requires a deep understanding of similarity: first, to say
