1 / 16

CHAPTER 7. LOGICAL AGENT

CHAPTER 7. LOGICAL AGENT. 석사 1 차 지 애 띠. OUTLINE. KNOWLEDGE-BASED AGENTS THE WUMPUS WORLD LOGIC PROPOSITIONAL LOGIC AGENT BASED ON PROPOSITIONAL LOGIC. KNOWLEDGE-BASED AGENTS. Knowledge Base - a set of representations of facts about the world

joelle-harmon
Télécharger la présentation

CHAPTER 7. LOGICAL AGENT

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 7.LOGICAL AGENT 석사 1차 지 애 띠

  2. OUTLINE • KNOWLEDGE-BASED AGENTS • THE WUMPUS WORLD • LOGIC • PROPOSITIONAL LOGIC • AGENT BASED ON PROPOSITIONAL LOGIC

  3. KNOWLEDGE-BASED AGENTS • Knowledge Base - a set of representations of facts about the world - a set of sentences that is expressed in a knowledge representation language • Knowledge-Based Agent deriving new sentence from old one Inference engine Knowledgebase

  4. KNOWLEDGE-BASED AGENTS • Outline of a knowledge-Based Agent • First, it TELLs the KB what it perceives (a way to add new sentences to the KB) • Second, it ASKs the KB what action it should perform (a way to query what is known) function KB-AGENT(percept) returns an action static:KB, a knowledge base t, a counter, initially 0, indicating time TELL(KB, MAKE-PERCEPT-SENTENCE(percept,t)) action - ASK(KB, MAKE-ACTION-QUERY(t)) TELL(KB, MAKE-ACTION-SENTENCE(action,t)) t t + 1 returnaction

  5. THE WUMPUS WORLD • Performance measure • Environment • Actuators – turn left, turn right, die, forward, grab, shoot • Sensors • the agent will perceive a stench in the square containing the wumpus and the directly adjacent squares • the agent will perceive a breeze in the squares directly adjacent to a pit • the agent will perceive a glitter in the square where the gold is • the agent will perceive a bump when it walks into a wall • the agent will perceive a scream anywhere in the cave when the wumpus is killed.

  6. A = Agent B = Breeze G = Glitter, Gold OK = Safe square P = Pit S = Stench V = Visited W = Wumpus THE WUMPUS WORLD

  7. P? P? W! S G V OK OK P? V V S OK OK P? P! V B V THE WUMPUS WORLD 1, 4 2, 4 3, 4 4, 4 A = Agent B = Breeze G = Glitter, Gold OK = Safe square P = Pit S = Stench V = Visited W = Wumpus 1, 3 2, 3 3, 3 4, 3 1, 2 2, 2 3, 2 4, 2 1, 1 2, 1 3, 1 4, 1 A

  8. LOGIC • Logic • formal language for provided the syntax and semantics are defined precisely • Syntax - the sentences in the language ex) x  y • Semantics - the “meaning” of sentences ex) x  y is false when y is bigger than x, and true otherwise • Model – possible world

  9. i i i LOGIC • KB  :“KB entails ” KB entails sentence  if and only if  is true in all worlds where KB is true • KB  :“ is derived from KB by i” or “i derives  from KB” • Soundness i is sound if whenever KB , it is also true that KB  • Completeness i is complete ifwhenever KB , it is also true that KB 

  10. PROPOSITIONAL LOGIC : Syntax • Logical constant : True or False • Logical connective → ∧ | ∨ | ⇒ | ⇔| ㄱ • BNF(Bacus-Naur Form) • Sentence  AtomicSentence | ComplexSentence • AtomicSentence  True | False | Symbol • Symbol  P | Q | R | … • ComplexSentence ㄱSentence • | Sentence ∧ Sentence • | Sentence ∨ Sentence • | Sentence ⇒ Sentence • | Sentence ⇔ Sentence

  11. P Q ㄱP P∧Q P∨Q P⇒Q P⇔Q False False True False False True True False True True False True True False True False False False True False False True True False True True True True PROPOSITIONAL LOGIC : Semantics • Truth Table • Equivalence, Validity, & Satisfiability • Two sentences are equivalence if they are true in the same set of models • A sentence is valid if it it true in all models • A sentence is satisfiable if it is true in some model • A sentence is unsatisfiable if it is true in no models

  12. α∨β, ㄱβ∨γ α∨γ ㄱα⇒β, β⇒γ ㄱα⇒γ = PROPOSITIONAL LOGIC : Inference • Modus Ponens (=Implication-Elimination) • And-Elimination • Double-Negation Elimination • Unit Resolution • Resolution α⇒ β, α β α1∧α2∧α3∧...∧αn αi ㄱㄱα α α∨β, ㄱβ α

  13. 1,4 2,4 3,4 4,4 1,3 W! 2,3 3,3 4,3 1,2 A S OK 2,2 OK 3,2 4,2 1,1 V OK 2,1 B V OK 3,1 P! 4,1 AGENT BASED ON PROPOSITIONAL LOGIC • Current state ㄱS1,1ㄱS2,1 S1,2 ㄱB1,1 B2,1ㄱB1,2 • Rules • R1 ㄱS1,1⇒ ㄱW1,1∧ㄱW1,2∧ㄱW2,1 • R2 ㄱS2,1⇒ ㄱW1,1∧ㄱW2,1∧ㄱW2,2∧ㄱW3,1 • R3 S1,2⇒ W1,3∨W1,2∨W2,2∨W1,1

  14. AGENT BASED ON PROPOSITIONAL LOGIC • 1. Modus Ponens & And-Elimination : ㄱS1,1 & R1   ㄱW1,1 ㄱW1,2ㄱW2,1 • 2. Modus Ponens & And-Elimination : ㄱS2,1 & R2 ㄱW2,2 ㄱW2,1 ㄱW3,1 • 3. Modus Ponens : S1,2 & R4  W1,3∨W1,2∨W2,2∨W1,1 • 4. Unit Resolution α : W1,3∨W1,2∨W2,2 β : W1,1 (ㄱW1,1 from 1)  W1,3∨W1,2∨W2,2 • 5. Unit Resolution α : W1,3∨W1,2∨W2,2 β : W2,2 (ㄱW2,2 from 2)  W1,3∨W1,2 • 6. nit Resolution α : W1,3∨W1,2 β : W1,2 (ㄱW1,2 from 2)  W1,3

  15. AGENT BASED ON PROPOSITIONAL LOGIC • Finding pits and wumpuses using logical inference • A knowledge base that states the “physics” of the wumpus world : ㄱP1,1 and ㄱW1,1 • Bx,y ⇔ (Px,y+1 ∨ Px,y-1 ∨ Px+1,y ∨ Px-1,y) • Sx,y ⇔ (Wx,y+1 ∨ Wx,y-1 ∨ Wx+1,y ∨ Wx-1,y) • W1,1 ∨ W1,2 ∨ … ∨ W4,3 ∨ W4,4 - at least one • To say that there in at most one wumpus, we needs a total of 155 sentences containing 64 distinct symbols • Keeping track of location and orientation • Lx,y ∧ FacingRightt ∧ Forwardt ⇒ Lt+1x+1,y • Propositions need to depend on time • If a agent moves 100 steps, it needs 6400 rules

  16. SUMMARY • Propositional Logic • Syntax : formal structure of sentences • Semantics : truth of sentences • Validity & Inference • Problems of propositional logic • In First-order logic, 6400 propositional rules  1

More Related