This slide continues the discussion of expert systems and describes how they work. Their key elements are their knowledge base and their inference engine. Ask students to demonstrate an understanding of the difference between forward chaining and backward chaining. For example, given a hypothesized expert system to determine what to make for dinner, what would an inference engine with forward chaining begin with? (Example, is there chicken? Is there beef? Is there broccoli, etc.? What are all the ingredients available and what could be made from them?) What would an inference with backward chaining begin with? (We are making chicken with broccoli. Do we have the ingredients?)