No one realized that the book and the labyrinth were one and the same. —Jorge Luis Borges "The Garden of Forking Paths"
I remember the summer of 1989. I was 19 years old, a sophomore biology major at Tufts University, and a transient in the home of my parents. My passions were, in no particular order, soccer, girls, literature, beer, and artificial intelligence. My summer began in the environmental lab of the Millstone nuclear power plant, where I measured the impact of thermal discharge on marine biodiversity. By day, I studied sand under a microscope, and by night, the works of Dostoevsky, Turing, Hofstadter, and Dennett.
That August, we took a family vacation to France and England. I left the sand behind, but the self-reflections of The Mind's I and the eternal golden braids of Gödel, Escher, Bach traveled with us. In fact, one of my fondest memories is of wandering with my brother through strange loops and tangled hierarchies, surrounded by the rolling green hills of the English countryside. Thinking machines, disembodied minds, silicon souls, selfish memes: we were intoxicated by metaphorical fugues, and a few pints from the local pub.
It was during these forays into artificial intelligence (AI) that I first stumbled into decision trees . A decision tree, like that shown in Figure 7-1, is a graph of choices and possible consequences. In theory, by identifying options and outcomes, and multiplying the probability and value (minus cost) of each outcome, ...