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Logical Reasoning I

Logical Reasoning I. Lecture 4-2 January 25 th , 1999 CS250. Announcements. Unix classes Office hours today TA (Office hours,Style) Quiz Midterm on Tuesday of 6th Week Project descriptions by email by end of week Lisp for Windows. A Little Lisp. What about progn ? Validity checking?.

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Logical Reasoning I

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

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

  3. A Little Lisp • What about progn? • Validity checking? CS250: Intro to AI/Lisp

  4. Designing an Interplanetary Explorer • Goals for the explorer • Actions we can take • Situations that might arise Can we anticipate everything? CS250: Intro to AI/Lisp

  5. Telling Your Computer about the World • What you know • How to go from what you know to what you don’t know • Will Rogers CS250: Intro to AI/Lisp

  6. 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 CS250: Intro to AI/Lisp

  7. 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) CS250: Intro to AI/Lisp

  8. Tell-Ask.lisp I ;;;; 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 '())) CS250: Intro to AI/Lisp

  9. Tell-Ask.lisp II ;;; 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+)))) CS250: Intro to AI/Lisp

  10. Tell-Ask.lisp III ;;; 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 CS250: Intro to AI/Lisp

  11. 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 CS250: Intro to AI/Lisp

  12. 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 CS250: Intro to AI/Lisp

  13. 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 CS250: Intro to AI/Lisp

  14. Separate Domain-Specific from the General CS250: Intro to AI/Lisp

  15. Wumpus World CS250: Intro to AI/Lisp

  16. Specifying the Wumpus World • Percepts? • Actions? • Goals? CS250: Intro to AI/Lisp

  17. Describing the Wumpus World • Is the world… • Deterministic • Fully accessible • Static • Discrete CS250: Intro to AI/Lisp

  18. One Environment is Easy • If we know the environment well, can engineer it • Range of environments? CS250: Intro to AI/Lisp

  19. Exploring the world Perception: Stench, Breeze, Glitter, Bump, Scream Perceive: [None, None, None, None, None] CS250: Intro to AI/Lisp

  20. Move Forward to 2,1 CS250: Intro to AI/Lisp

  21. Perception after One Move Stench: None Breeze: Yes Glitter: None Bump: None Scream: None CS250: Intro to AI/Lisp

  22. What Does the World Look Like? CS250: Intro to AI/Lisp

  23. 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? CS250: Intro to AI/Lisp

  24. 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 CS250: Intro to AI/Lisp

  25. Logical Committment CS250: Intro to AI/Lisp

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