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Introduction to AI & AI Principles (Semester 1) WEEK 4 – Wednesday (2008/09)

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.

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Introduction to AI & AI Principles (Semester 1) WEEK 4 – Wednesday (2008/09)

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  1. 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

  2. Reminder(HOT) DRINKSCase StudyPlanning the Delivery of One Drink

  3. Planning the Delivery of One Drink, 1 • Initial 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. • Other Facts: • F is in K • K and S are connected by door D-KS • K and the hall (H) are connected by door D-KH • H and S are connected by door D-HS. • Goal Situation (for You to achieve): • M has B; B is open.

  4. Planning the Delivery of One Drink, 2 • Actions available (at a high level): • agent aopens a bottle b with a bottle-opener o. • agent aopens a door d. • agent acloses a door d. • agent agoes through a room-door e. • agent amoves from (being next to) an object x to an object y. • agent apicks up an object x with one free hand. • agent apicks up an object x with both hands. • agent aputs down an object y. • agent agives a held object z to agent p. • NB: In most cases you will act as agent a, but we should be open to other possibilities.

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

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

  7. New Stuff on(HOT) DRINKSCase StudyPlanning the Delivery of One Drink

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

  9. Planning the Delivery of One Drink, 6(corrected) • What Do You Need to Know about the action • agent a goes through a room-door e [joining rooms r1 & r2] ?? • Answer: • Preconditions: • e is open • a is next to e. • a is in r1(say). • (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 !!))

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

  11. Planning the Delivery of One Drink, 8 • A possible way of working out an action sequence: • How do I achieve the Goal? I could address the following two subgoals separately: • (G1) M has B; (G2) B is open. • 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. • How do I achieve G1.1? Aha , …..

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

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