Logical Agents. Russell and Norvig: Chapter 7 CMSC 421 – Fall 2006. “Thinking Rationally”. Computational models of human “thought” processes Computational models of human behavior Computational systems that “think” rationally Computational systems that behave rationally. sensors.
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Russell and Norvig: Chapter 7CMSC 421 – Fall 2006
environment
?
agent
actuators
Knowledge base
Inference Engine
Domain-independent algorithms
Knowledge-Based AgentDomain-specific content
Knowledge Base: set of sentences represented in a knowledge representation language and represents assertions about the world.
Inference rule: when one ASKs questions of the KB, the answer should follow from what has been TELLed to the KB previously.
ask
tell
[1,1] The KB initially contains the rules of the environment. The first percept is [none, none,none,none,none], move to safe cell e.g. 2,1
[2,1] breeze which indicates that there is a pit in [2,2] or [3,1], return to [1,1] to try next safe cell
[1,2] Stench in cell which means that wumpus is in [1,3] or [2,2]
YET … not in [1,1]
YET … not in [2,2] or stench would have been detected in [2,1]
THUS … wumpus is in [1,3]
THUS [2,2] is safe because of lack of breeze in [1,2]
THUS pit in [3,1]
move to next safe cell [2,2]
[2,2] move to [2,3]
[2,3] detect glitter , smell, breeze
THUS pick up gold
THUS pit in [3,3] or [2,4]
Sentences
Sentences
represent
represent
Conceptualization
World W
Facts about W
Facts about W
hold
hold
Connection World-RepresentationKB |=
M()
M(KB)
i is sound if whenever KB |-i it is also true that KB|=
i is complete if whenever KB |= it is also true that KB|-i
Valid sentences: true, :false, P Ç: P
Satisfiable sentences: P, true, : P
Unsatisfiable sentences: P Æ: P, false, :true
((P Ç H) Æ:H) ) P
P
H
((P
H)
H) )
P
P
H
(P
H)
H
Ç
Ç
Æ
:
Ç
Æ
:
T
T
T
F
T
T
F
T
T
T
F
T
T
F
T
F
F
F
F
T
a Æba
aÇb:bÇg a Çg
Examples in Wumpus WorldProve A ) B, (A Æ B) ) C, Therefore A ) C
clause
Conjunctive Normal FormExample: (A Ç B) , (C ) D)
((A Ç B) ) (C ) D)) Æ ((C ) D) ) (A Ç B)
(: (A Ç B) Ç (: C Ç D)) Æ (: (: C Ç D) Ç (A Ç B) )