And Or Trees for Expert Systems

• Use And Or trees for subgoals
• To achieve X, you have to do A, B, and C
• To achieve A, you have to do I, J or K
• of course you may have to do (I and J) or K
• So you can describe your ES using an And-Or tree
• Coffee example:
  • The root is have coffee
  • The subgoals are, (buy it) or (make it) or (get someone else to get it)
  • To (buy it) you have to (have money) and (be at shop)
  • What does this tree look like?
• Expand the tree.
• You can use an and-or tree for other things, but generally it works well with goals
• And-or trees are a good description of backward chaining systems.