Expert systems represent a practical application of artificial intelligence (AI) research that has been going on for almost the entire history of general-purpose computing. Much has been learned about how we store knowledge and combine what we know to derive new results and solve problems. Expert systems based on these ideas take many forms. The rule-based system used in the examples on this Web site represents knowledge with of production rules -- so named because new facts are produced when a rule is proven true. The next slide shows some sample rules used to diagnose why a car won't start.