Sample Production System

An Example of a Production System, Adapted from Winston 1977: 357-366.

1. Problem: Moving furniture

2. WM: Finite size (e.g., 7 items, or extend to 11);
            Begins with goal; e.g., (put-at table loc1)

3. Productions (executed in order):
   • P1: converts request to put object on support
           into command to put it at some location

     IF  : (put-on $object $support)
            ;; i.e., if WM contains (put-on ...)
     THEN: mark (first WM);
            ;; "mark" implements "remove" by marking the WM entry so that it won't be matched
           add (put-at *object (space on *support)).
            ;; "add" puts item at front of WM & moves other items down;
                     ;; overflow falls off
     

   • P2: expands goal to put object at location
           into "grasp" goals and remembered target locations

     IF  : (put-at $object $newplace)
     THEN: mark (first WM);
           add (target *object *newplace);
           add (grasp *object).

   • P3: helps to forget invalidated support relations

     IF  : (move $object);
           ($support supports *object)
     THEN: mark (*support supports *object).

   • P4: moves hand with object & ungrasps it

     IF  : (move $object)
     THEN: mark (first WM);
           notice (target *object $newplace);
            ;; "notice" moves item to front of WM
           do (move-hand *newplace);
           do (ungrasp).

   • P5: moves free hand to object & grasps it

     IF  : (grasp $object);
           (*object supports nothing);
            ;; items must be in WM in that order
     THEN: mark (first WM);
           add (move *object);
           do (move-hand (top-of *object));
           do (grasp *object).

   • P6: moves obstacles out of the way

     IF  : (grasp $object);
           (*object supports $obstruction)
     THEN: add (put-on *obstruction floor).

   • P7: identifies obstacles

     IF  : (grasp $object)
     THEN: find (*object supports ?x);
           notice (grasp *object).
     

4. Click Here for an Example (in Excel)

5. Exercises:
   1. What happens if
      find (*object supports ?x)

      in P7 returns

      (table supports lamp)?

   2. What happens in the previous situation if WM can hold at least 11 items?

   3. What happens if, instead of "(*object supports nothing)" in P5, we used negation by failure:
      IF  : (grasp $object);
            not (*object supports $obstruction);
      THEN: mark (first WM);
            add (move *object);
            do (move-hand (top-of *object));
            do (grasp *object).

   4. Implement this system in Lisp (or your favorite programming language).
      • For implementation hints in an old version of Lisp, see Winston 1977: 360-366.

   5. (Hard) Implement this system in SNePS.
      • Hint: You may need to make use of the SNePS Rational Engine (SNeRE), which turns SNePS into a knowledge-representation, reasoning, and acting system!

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