Lecture 4-1CS250: Intro to AI/Lisp Logical Reasoning I Lecture 4-2 January 25 th, 1999 CS250

Lecture 4-1CS250: Intro to AI/Lisp Announcements Unix classes Office hours today TA (Office hours,Style) Quiz Midterm on Tuesday of 6th Week Project descriptions by by end of week Lisp for Windows

Lecture 4-1CS250: Intro to AI/Lisp A Little Lisp What about progn ? Validity checking?

Lecture 4-1CS250: Intro to AI/Lisp Designing an Interplanetary Explorer Goals for the explorer Actions we can take Situations that might arise

Lecture 4-1CS250: Intro to AI/Lisp Telling Your Computer about the World What you know How to go from what you know to what you don’t know Will Rogers

Lecture 4-1CS250: Intro to AI/Lisp Knowledge Base Knowledge base:Database :: Knowledge:Data KB stores what the computer knows about the world Knowledge representation language –How we encode knowledge about the world –Each bit of knowledge is a sentence

Lecture 4-1CS250: Intro to AI/Lisp Getting through to your computer KB Interaction –Tell: Add new sentences to the KB –Ask: Query what’s known (or what follows from what is known)

Lecture 4-1CS250: Intro to AI/Lisp ;;;; Main Functions on KBs: Tell, Retract, Ask-Each, ;;;; Ask, Ask-Pattern[s] ;;; First we define a very simple kind of knowledge base, ;;; literal-kb, that just stores a list of literal sentences. (defstructure literal-kb "A knowledge base that just stores a set of literal sentences." (sentences '())) Tell-Ask.lisp I

Lecture 4-1CS250: Intro to AI/Lisp ;;; There are three generic functions that operate on ;;; knowledge bases, and that must be defined as methods ;;; for each type of knowledge base: TELL, RETRACT, and ;;; ASK-EACH. Here we show the implementation for literal-kb; ;;; elsewhere you'll see implementations for propositional, ;;; Horn, and FOL KBs. (defmethod tell ((kb literal-kb) sentence) "Add the sentence to the knowledge base." (pushnew sentence (literal-kb-sentences kb) :test #'equal)) (defmethod retract ((kb literal-kb) sentence) "Remove the sentence from the knowledge base." (deletef sentence (literal-kb-sentences kb) :test #'equal)) (defmethod ask-each ((kb literal-kb) query fn) "For each proof of query, call fn on the substitution that the proof ends up with." (declare (special +no-bindings+)) (for each s in (literal-kb-sentences kb) do (when (equal s query) (funcall fn +no-bindings+)))) Tell-Ask.lisp II

Lecture 4-1CS250: Intro to AI/Lisp ;;; There are three other ASK functions, defined below, ;;; that are defined in terms of ASK-EACH. These are ;;; defined once and for all here (not for each kind ;;; of KB)." (defun ask (kb query) "Ask if query sentence is true; return t or nil." (ask-each kb (logic query) #'(lambda (s) (declare (ignore s)) (RETURN-FROM ASK t)))) ;;; Omitted pattern-matching ASK’s Tell-Ask.lisp III

Lecture 4-1CS250: Intro to AI/Lisp Knowledge-Based Agents  Agents perceive the world around them  Perceptions are recorded in the KB  Actions are chosen based on the KB  Results of actions are recorded

Lecture 4-1CS250: Intro to AI/Lisp Levels of Agents Knowledge level –What an agent knows –Planetary core samples must be taken at least 100mm below the surface Logical level –Knowledge is encoded at this level –MinDepth(CoreSample,100) Implementation level –Inside the machine

Lecture 4-1CS250: Intro to AI/Lisp Building Knowledge Agents Lean on the inference mechanism –Tell agent what it needs to know Declarative –Declare the state of the world, and let ‘er rip Adding learning –Reacting to percepts

Lecture 4-1CS250: Intro to AI/Lisp Separate Domain-Specific from the General

Lecture 4-1CS250: Intro to AI/Lisp Wumpus World

Lecture 4-1CS250: Intro to AI/Lisp Specifying the Wumpus World Percepts? Actions? Goals?

Lecture 4-1CS250: Intro to AI/Lisp Describing the Wumpus World Is the world… –Deterministic –Fully accessible –Static –Discrete

Lecture 4-1CS250: Intro to AI/Lisp One Environment is Easy If we know the environment well, can engineer it Range of environments?

Lecture 4-1CS250: Intro to AI/Lisp Exploring the world Perceive: [None, None, None, None, None] Perception: Stench, Breeze, Glitter, Bump, Scream

Lecture 4-1CS250: Intro to AI/Lisp Move Forward to 2,1

Lecture 4-1CS250: Intro to AI/Lisp Perception after One Move Stench: None Breeze:Yes Glitter:None Bump:None Scream:None

Lecture 4-1CS250: Intro to AI/Lisp What Does the World Look Like?

Lecture 4-1CS250: Intro to AI/Lisp Knowledge Representation Not just computer readable… …computer reasonable as well Syntax - Rules for building expressions Semantics - Relationship between facts in the world and sentences Examples?

Lecture 4-1CS250: Intro to AI/Lisp Entailment What follows from what Entailment is relationship among sentences –KB entails a “Follows” is a relationship among facts in the world Inference procedures that generate only entailed sentences is sound

Lecture 4-1CS250: Intro to AI/Lisp Logical Committment