Introduction to AI & AI Principles (Semester 1) WEEK 4 – Wednesday Introduction to AI & AI Principles (Semester 1) WEEK 4 – Wednesday (2008/09) John Barnden Professor of Artificial Intelligence School of Computer Science University of Birmingham, UK

Reminder (HOT) DRINKS Case Study Planning the Delivery of One Drink

Planning the Delivery of One Drink, 1 uInitial Situation: Mike (M) wants beer; Mike is in the sitting room (S); you are in the kitchen (K); there is an unopened bottle B of beer in the fridge (F); you are next to F; there is a bottle-opener O on top of F; doors D-KS, D-KH and D- HL[see below] are closed. uOther Facts: l F is in K l K and S are connected by door D-KS l K and the hall (H) are connected by door D-KH l H and S are connected by door D-HS. uGoal Situation (for You to achieve): l M has B; B is open.

Planning the Delivery of One Drink, 2 uActions available (at a high level): l agent a opens a bottle b with a bottle-opener o. l agent a opens a door d. l agent a closes a door d. l agent a goes through a room-door e. l agent a moves from (being next to) an object x to an object y. l agent a picks up an object x with one free hand. l agent a picks up an object x with both hands. l agent a puts down an object y. l agent a gives a held object z to agent p. uNB: In most cases you will act as agent a, but we should be open to other possibilities.

Planning the Delivery of One Drink, 3 uIndividual Exercise “One-Drink A” [4 mins] l Write down one sensible sequence of actions that will achieve the Goal from the Initial Situation. Use only actions from my list. l Write down another such sequence. uIndividual Exercise “One-Drink B” [3 mins] l How did you work out your first sequence, do you think?

Planning the Delivery of One Drink, 4 uOne sensible sequence of actions (or rather, action instances) is as follows…. and is there anything missing?: l I move to F. l I open F’s door. l I pick up B with one free hand. l I pick up O with one free hand. l I open B with O. l I put down O. l I move to D-KS. l I open D-KS. l I go through D-KS. l I move to M. l I give B to M. uNB: we instantiated the variables in the action specifications by replacing them by constants.

New Stuff on (HOT) DRINKS Case Study Planning the Delivery of One Drink

Planning the Delivery of One Drink, 5 uWhat Do You Need to Know about the action agent a opens a bottle b with a bottle-opener o ?? uanswer: l [Some] Preconditions: b is unopened a is holding b [roughly upright]. a is holding o. l [Some] (Non-)Effects: b is open a is still holding b. a is still holding o.

Planning the Delivery of One Drink, 6 (corrected) uWhat Do You Need to Know about the action agent a goes through a room-door e [joining rooms r1 & r2] ?? uAnswer: l Preconditions: e is open a is next to e. a is in r1(say). l (Non-)Effects: a is in r2. [but what about r1?] a is [still] next to e [though in a different way]. ((e is still open)) [but do you need to know this?] ((e still joins rooms r1 and r2 !!))

Planning the Delivery of One Drink, 7 uIndividual Exercise “One-Drink C” [up to 10 mins] uWrite down What You Need to Know for the following actions: l a moves from (being next to) an object x to an object y. l a puts down an object y. l a gives a held object z to person p. l a picks up an object x with both hands. l a picks up an object x with one free hand.

Planning the Delivery of One Drink, 8 uA possible way of working out an action sequence: l How do I achieve the Goal? I could address the following two subgoals separately: (G1) M has B; (G2) B is open. l How do I achieve, say, G1? Aha, an action that could achieve it is “a gives held object z to person p”, with a instantiated to me, z instantiated to B, and p instantiated to M. But this means I have to achieve two subgoals (and not forget about G2): (G1.1) I am holding B; (G1.2) I am next to M. l How do I achieve G1.1? Aha, …..

Planning the Delivery of One Drink, 9 uSuch a process is a form of backwards chaining. uNotice some complications: l Trying to achieve more than one subgoal. One issue: what order to address them in? l The fact that several different action instances could achieve a particular subgoal. How do you choose? What order? l In principle, a single action instance could achieve more than one subgoal. l Needing to remember other subgoals when thinking backwards through an action instance (subgoal regression).