Backward Chaining

• Backward Chaining means chaining back from the goal, to apply rules that meet the goal.
• As with Forward Chaining there are rules and WM.
• However there is also a goal stack.
• So given the rules
• if (have money) and (at coffee-shop) then (lose 75p) and (have coffee)
• if (have water) and (have ground coffee) and (have cofee-machine) then (have coffee)
• if (at office) and (can walk) then (at coffee-shop)
• if WM = (have money) and (at coffee-shop)
• set the goal, then apply the first rule
• if WM = (have money) and (at office) and (can walk)
• set the goal (have coffee)
• try to apply the first rule
• add (at coffee-shop) to stack
• apply third rule, and pop the stack
• apply first rule and achieve the ultimate goal
• In class exercise:
  1. Simulate a run of this system forward
  2. What data items do you need?
  3. Simulate a run of this system backward
  4. What data items are you prompted for