Agents That Communicate Chris Bourne Chris Christen Bryan Hryciw
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Agents That CommunicateChris Bourne
Chris Christen
Bryan Hryciw
7/31/2019 09.1 Communication
http://slidepdf.com/reader/full/091-communication 2/53
OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation Ambiguity and Disambiguity
A Communicating Agent
Summary
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IntroductionCommunication is the intentional exchange of informationbrought about by the production and perception of signs drawnfrom a shared system of conventional signs.
Most animals employ a fixed set of signs to represent messagesthat are important to their survival: food here, predator nearby,approach, withdraw, let’s mate.
Humans, just as many other animals, use a limited number of signs to communicate (smiling, shaking hands)
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IntroductionHumans are the only animal that has developed a complex,structured system of signs, known as language, that enables usto communicate most of what they know about the world.
Although other animals such as chimpanzees and dolphins haveshown vocabularies of hundreds of symbols, humans are theonly species that can communicate an unbounded number of qualitatively different messages.
Although there are other uniquely human attributes, such aswearing clothes and watching TV, Turing created his test basedon language because language is closely tied to thinking, in away these other attributes are not.
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Origins & Evolution of Language
Did humans develop the use of language because weare smart, or are we smart because we use language
well?
Jerrison, 1991: Human language stems from a need for bettercognitive maps of territory. Canines rely heavily on scentmarking and their sense of smell to determine where they areand what other animals have been there. Since primates do nothave such a highly developed sense of smell, they substitutedvocal sounds for scent marking.
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Communication as ActionSpeech Act:
The action available to an agent to produce language
includes talking, typing, sign language, etc.Speaker - An agent that produces a speech act
Hearer - An agent that receives a speech act
Why would agents choose to perform a speech act?
To be able to:
• Inform, Query, Answer, Request or Command, Promise, Acknowledge and Share
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Communication as ActionMake the Hearer take some action:
Promise:
to do things or offer deals. Ex. I’ll shoot the wumpus if you let me share the gold.
Query:
other agents about particular aspects of the world. Ex. Have you smelled the wumpus anywhere?
Request or Command: other agents to perform actions. It can be seen as impolite tomake direct requests, so often an indirect speech act (a requestin the form of a statement or question) is used instead. Ex. I could use some help carrying this or Could you please help me carry this?
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Difficulties with CommunicationSpeaking:
When is a speech act called for?
Which speech act, out of all the possibilities is the right one?
Nondeterminism
Understanding:
Given ambiguous inputs, what state of the world could havecreated these inputs?
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Fundamentals of LanguageFormal Languages: Languages that are inventedand are rigidly defined. A set of strings where each
string is a sequence of symbols taken from a finiteset called the terminal symbols.
Lisp, C++, first order logic, etc.
Natural Languages: Languages that humans useto talk to one another.
Chinese, Danish, English, etc.
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Component Steps of CommunicationThree steps take place in the speaker:
Intention: S want H to believe P
Generation: S chooses words W
Synthesis: S utters the words W
Four steps take place in the hearer:
Perception: H perceives W1 (ideally, W = W1)
Analysis: H infers that W1 has possible meanings P1, … , Pn Disambiguation: H infers that S intended to convey Pi (ideally,Pi = P)
Incorporation: H decides to believe Pi (or rejects it if it is outof line with what H already believes)
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Models of CommunicationEncoded Message Model:
Speaker encodes a proposition into words or signs. The hearerthen tries to decode this message to retrieve the original
proposition. The meaning in the speaker’s head, the message thatgets transmitted, and the interpretation that hearer arrives at areall the same, unless there is noise during communication, or anerror in encoding or decoding occurs.
Situated Language Model:
Created because of limitations on the encoded message model.The meaning of the message depends on both the words, and thesituation.
Ex. “Diamond” refers to one thing when the subject is jewelry,and a completely different meaning when the subject is baseball.
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Types of Communicating AgentsCommunicating using Tell and ask:
Agents share a common internal representation language
Agents are capable of communicating without any external
language at all
Communicating using Formal Language:
Agents make no assumptions about each other’s internal
language Agents share a communication language that is a subset of English
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Tell and Ask Communication with Tell and Ask
Percepts Actions Percepts Actions
Reasoning Reasoning
KB KB
Agent A Agent B
TELL(KBB , “P”) TELL(KBA , “P”)
ASK(KBB , “Q”) TELL(KBB , “Pit (PA1) At (PA1,[2,3], SA9)”)
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Formal Language
Percepts Actions Percepts ActionsReasoning Reasoning
KB KB
Agent A Agent B Language
Language
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of English Syntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Formal Grammar for a Subset of EnglishLexicon: List of allowable vocabulary words.
Noun -> stench | breeze | glitter | nothing | wumpus | pit | pits | gold | east | …
Verb -> is | see | smell | shoot | feel | stinks | go | grab | carry | kill | turn | …
Adjective -> right | left | east | south | back | smelly | …
Adverb -> here | there | nearby | ahead | right | left | east | south | back | …
Pronoun -> me | you | I | it | …
Name -> John | Mary | Boston | Aristotle | … Article -> the | a | an | …
Preposition -> to | in | on | near | … Conjunction -> and | or | but | …
Digit -> 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
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Formal Grammar for a Subset of English
NP -> Pronoun
-> Noun
-> Article Noun
-> Digit Digit
-> NP PP
-> NP RelClause
RelClause -> that VP
VP -> Verb
-> VP NP
-> VP Adjective
-> VP PP
-> VP Adverb
PP -> Preposition NP
Grammar:
S -> NP VPS -> S Conjunction S
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Parsing AlgorithmsThere are many algorithms for parsing
Top-down parsing
• Starting with an S and expanding accordingly
Bottom-up parsing
Combination of top-down and bottom-up
Dynamic programming techniques• Avoids inefficiencies of backtracking
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Bottom-up Parse (example)
function BOTTOM-UP-PARSE(words, grammar ) returns a parse tree
forest words
loop do
if LENGTH( forest ) = 1 and CATEGORY( forest [1]) = START(grammar ) then
return forest [1]else
i choose from {1…LENGTH( forest )}
rule choose from RULES(grammar)
n LENGTH(RULE-RHS(rule))
subsequence SUBSEQUENCE( forest, i, i+n-1)
if MATCH(subsequence,RULE-RHS(rule)) then
forest[i…i+n-1] [MAKE-NODE(RULE-LHS(rule) , subsequence)]
else fail
end
forest subsequence rule
The wumpus is dead Article wumpus is dead
Article Noun is dead
NP is dead
NP Verb dead
NP Verb Adjective
NP VP Adjective
NP VP
S
Thewumpus
Article Noun
is
dead
Verb
VP Adjective
NP VP
Article the Noun wumpus
NP Article Noun
Verb is
Adjective dead
VP Verb
VP Verb Adjective
S NP VP
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Definite Clause Grammer (DCG)Problems with Backus-Naur Form (BNF)
Need meaning
Context sensitive
Introduction of First Order Logic
BNF First Order Logic
S NP VP NP(s1) /\ VP(s2) S(Append(s1 ,s2))
Noun stench | … (s=“stench” \ / …) Noun(s)
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DCG NotationPositive:
Easy to describe grammars
Negative:
More verbose than BNF
3 Rules:•The notation X Y Z … translate as Y(s1) /\ Z(s2)… X(Append(s1, s2,…).
•The notation X word translates as X([“word ”]).
•The notation X Y | Z | … translates as Y’(s) \ / Z’(s) \ /… X(s), where Y’
is the translation into logic of the DCG expression Y.
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Extending the NotationNon-terminal symbols can be augmented
A variable can appear on RHS
An arbitrary logical test can appear on RHS
DCG First Order Logic
Digit (sem) sem { 0 sem 9 }
Number (sem) Digit (sem)
Number (sem) Number (sem1) Digit (sem2)
{sem = 10 sem1 + sem2}
(s=[sem]) Digit (sem , s)
Digit (sem , s) Number (sem , s)
Number (sem , s1) /\ Digit (sem , s2) /\
sem = 10 sem1 + sem2
Number (sem , Append (s1 , s2)
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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OvergenerationSimple grammar can overgenerate
Ex: “Me smells a stench.”
To fix we must understand
Cases of English
Nominative - subjective - “I” Accusative - objective - “me”
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New Rules
Use of Augmentation
S NP(case)
VP
PP
Pronoun(Subjective) Pronoun(Objective)
NP(subjective) VP | … Pronoun(case) | Noun | Article Noun
VP NP(Objective) | …
Preposition NP(Objective)
I | you | he | she | …
me | you | him | her | …
Changes needed to handle subjective and objective cases
S
NPs
Npo
VPPP
Pronouns
Pronouno
NPs VP | …
Pronouns | Noun | Article Noun
Pronouno | Noun | Article Noun
VP NPo | … Preposition NPo
I | you | he | she | …
me | you | him | her | …
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Verb SubcategorizationNow have slight improvement
Must create a sub-categorization listVerb Subcats Example
give [NP , PP]
[NP , NP]
give the gold in 3,3 to me
give me the gold
smell [NP]
[Adjective][PP]
smell a wumpus
smell awfulsmell like a wumpus
is [Adjective]
[PP]
[NP]
Is smelly
is in 2 2
is a pit
believe [S] Believe the smelly wumpus in 2 2 is dead
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Parse TreeS
NP
VP([])
VP([NP])
VP([NP,NP]) NP NP
Pronoun Pronoun Article NounVerb([NP,NP])
You give me the gold
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Semantic InterpretationSemantic Interpretation: Responsible for combiningmeanings compositionally to get a set of possible interpretations
Formal Languages
Compositional Semantics: The semantics of any phrase is afunction of its subphrases
• X + Y
We can handle an infinite grammar with a finite set of rules
Natural Languages
Appears to have a noncompositional semantics
• “The batter hit the ball”
Semantic interpretation alone cannot be certain of the right interpretation of a phrase or sentence
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Semantic InterpretationSemantics as DCG Augmentation
The same idea used to specify the semantics of numbersand digits can applied to the complete language of
mathematics
Exp(sem) – > Exp(sem1) Operator (op) Exp(sem2) {sem = Apply(op, sem1 , sem2)}
Exp(sem) – > ( Exp(sem) )
Exp(sem) – > Number (sem)
Digit(sem) – > sem { 0 sem 9 }
Number (sem) – > Digit (sem)
Number (sem) – > Number (sem1) Digit (sem2) { sem = 10 × sem1 + sem2 }
Operator (sem) – > sem { sem +, – ,×,÷}}
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The Semantics of E 1 Semantic structure is very different from syntactic structure.
We use an intermediate form called a quasi-logical form which uses a new construction which we will call a quantified
term. “every agent” -> [" a Agent (a)]
“Every agent smells a wumpus”
$ e (e Perceive([" a Agent (a)], [$ w Wumpus(w)], Nose) During( Now, e))
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Pragmatic InterpretationThrough semantic interpretation, an agent can perceive a stringof words and use a grammar to derive a set of possiblesemantic interpretations.
Now we address the problem of completing the interpretationby adding information about the current situation
Information which is noncompositional and context-dependant
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Pragmatic InterpretationIndexicals: Phrases that refer directly to the current situation
“I am in Boston today.”
Anaphora: Phrases referring to objects that have beenmentioned previously
“John was hungry. He entered a restaurant.”
“After John proposed to Marsha, they found a preacher and gotmarried. For the honeymoon, they went to Hawaii.”
Deciding which reference is the right one is a part of disambiguation.
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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Ambiguity and DisambiguationThe biggest problem in communicative exchange isthat most utterances are ambiguous .
Squad helps dog bite victim.
Red-hot star to wed astronomer.
Helicopter powered by human flies.
Once-sagging cloth diaper industry saved by full dumps.
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AmbiguityLexical Ambiguity
a word has more than one meaning
Syntactic Ambiguity (Structural Ambiguity)more than one possible parse for the phrase
Semantic Ambiguity
follows from lexical or syntactic ambiguity
Referential Ambiguitysemantic ambiguity caused by anaphoric expressions
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AmbiguityPragmatic Ambiguity
Speaker and hearer disagree on what the current situationis.
Local Ambiguity
A substring can be parsed several ways.
Vagueness
Natural languages are also vague
• “It’s hot outside.”
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DisambiguationDisambiguation is a question of diagnosis.
Models of the world are used to provide possibleinterpretations of a speech act.
Models of the speaker
Models of the hearer
It is difficult to pick the right interpretation becausethere may be several right ones.
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DisambiguationIn general, disambiguation requires the combinationof four models:
the world model
the mental model
the language model
the acoustic model
Natural language often uses deliberate ambiguity.
Most language understanding programs ignore thispossibility
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DisambiguationContext free grammars do not provide a very usefullanguage model.
Probabilistic context-free grammars (PCFG’s)
each rewrite rule has a probability associated with it
S – > NP VP (0.9)S – > S Conjunction S (0.1)
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OverviewCommunication as Action
Types of Communicating Agents
A Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)
Definite Clause Grammar (DCG)
Augmenting a Grammar
Semantic Interpretation
Ambiguity and Disambiguity
A Communicating Agent
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A Communicating Agent How does this all fit in to an agent that cancommunicate?
Start with the wumpus world robot slave.
Extend the grammar to accept commands
“Go east”
“Go to 2 2”
Identify the kind (i.e, command or statement) of speech as part of the quasi-logical form.
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A Communicating Agent Rules for commands and statementsS(Command (rel( Hearer )) – > VP(rel)
S(Statement (rel(obj)) – > NP(obj) VP(rel)
Rules for acknowledgementsS( Acknowledge(sem)) – > Ack (sem)
Ack (True) – > yes
Ack (True) – > OK
Ack (False) – > no
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Summary Agents send signals to each other using a speech act.
All animals use some conventional signs to communicate, buthumans use language in a more sophisticated way that enables
them to communicate much moreFormal language theory and phrase structure grammars areuseful tools for dealing with some aspects of natural language
Communication involves
three steps by the speaker
• intention, generation and synthesis
four steps by the hearer
• perception, analysis, disambiguation and incorporation
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SummaryThe encoded message model of communication says that aspeaker encodes a representation of a proposition intolanguage, and the hearer decodes the message to uncover the
propositionThe situated language model states that the meaning of amessage is a function of both the message and the situation inwhich it occurs.
Augmenting a grammar allows us to handle many problems
Definite Clause Grammar (DCG) is an extension of BNF that allowsfor augmentations
There are many algorithms for parsing strings.
I.e. bottom up, top down, combination, and dynamic
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SummaryPragmatic interpretation takes the current situation intoaccount to determine the effect of an utterance in context
Disambiguation is the process of deciding which of thepossible interpretations is the one that the speaker intended toconvey.
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The End
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BibliographyNorvig, Peter and Russell, Stuart, 1995. “ Artificial Intelligence A Modern Approach ”, Prentice-Hall Inc., Upper Saddle River, NewJersey.