Agents That Communicate Chris Bourne Chris Christen Bryan Hryciw.
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Transcript of Agents That Communicate Chris Bourne Chris Christen Bryan Hryciw.
Agents That Communicate
Chris Bourne
Chris Christen
Bryan Hryciw
OverviewCommunication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating AgentSummary
IntroductionCommunication is the intentional exchange of information brought about by the production and perception of signs drawn from a shared system of conventional signs.
Most animals employ a fixed set of signs to represent messages that 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)
IntroductionHumans are the only animal that has developed a complex, structured system of signs, known as language, that enables us to communicate most of what they know about the world.
Although other animals such as chimpanzees and dolphins have shown vocabularies of hundreds of symbols, humans are the only species that can communicate an unbounded number of qualitatively different messages.
Although there are other uniquely human attributes, such as wearing clothes and watching TV, Turing created his test based on language because language is closely tied to thinking, in a way these other attributes are not.
Origins & Evolution of Language
Did humans develop the use of language because we are smart, or are we smart because we use language well?
Jerrison, 1991: Human language stems from a need for better cognitive maps of territory. Canines rely heavily on scent marking and their sense of smell to determine where they are and what other animals have been there. Since primates do not have such a highly developed sense of smell, they substituted vocal sounds for scent marking.
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Communication as ActionSpeech Act:
The action available to an agent to produce languageincludes talking, typing, sign language, etc.Speaker - An agent that produces a speech actHearer - 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
Communication as ActionTransferring Information to Hearer:
Inform:each other about the part of the world each has explored, so other agent has less exploring to do. Ex. There’s a breeze in 3 4.
Answer:questions. This is a kind of informing. Ex. Yes, I smelled the wumpus in 2 3.
Acknowledge: requests and offers. Ex. Okay.
Share:feelings and experiences with each other. Ex. You know, that wumpus sure needs deodorant.
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
to make direct requests, so often an indirect speech act (a request in 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?
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 have created these inputs?
Fundamentals of Language
Formal Languages: Languages that are invented and are rigidly defined. A set of strings where each string is a sequence of symbols taken from a finite set called the terminal symbols.
Lisp, C++, first order logic, etc.
Natural Languages: Languages that humans use to talk to one another.
Chinese, Danish, English, etc.
Component Steps of CommunicationThree steps take place in the speaker:
Intention: S want H to believe PGeneration: S chooses words WSynthesis: 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 out of line with what H already believes)
Models of CommunicationEncoded Message Model:
Speaker encodes a proposition into words or signs. The hearer then tries to decode this message to retrieve the original proposition. The meaning in the speaker’s head, the message that gets transmitted, and the interpretation that hearer arrives at are all the same, unless there is noise during communication, or an error 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 the situation. Ex. “Diamond” refers to one thing when the subject is jewelry, and a completely different meaning when the subject is baseball.
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Types of Communicating AgentsCommunicating using Tell and ask:
Agents share a common internal representation languageAgents are capable of communicating without any external language at all
Communicating using Formal Language:Agents make no assumptions about each other’s internal languageAgents share a communication language that is a subset of English
Tell and AskCommunication with Tell and Ask
Percepts Actions Percepts Actions
Reasoning Reasoning
KB KBAgent A Agent B
TELL(KBB, “P”) TELL(KBA, “P”)
ASK(KBB, “Q”) TELL(KBB, “Pit(PA1) At(PA1,[2,3], SA9)”)
Formal Language
Percepts Actions Percepts ActionsReasoning Reasoning
KB KBAgent A Agent BLanguage
Language
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
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
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
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Parsing Algorithms
There are many algorithms for parsing
Top-down parsing• Starting with an S and expanding
accordingly
Bottom-up parsingCombination of top-down and bottom-upDynamic programming techniques• Avoids inefficiencies of backtracking
Bottom-up Parse (example)
function BOTTOM-UP-PARSE(words, grammar) returns a parse tree
forest wordsloop 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 failend
Article theNoun wumpusNP Article NounVerb isAdjective deadVP VerbVP Verb AdjectiveS NP VP
ThewumpusArticle NounisdeadVerbVP AdjectiveNP VP
The wumpus is deadArticle wumpus is deadArticle Noun is deadNP is deadNP Verb deadNP Verb AdjectiveNP VP AdjectiveNP VPS
rulesubsequenceforest
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Definite Clause Grammer (DCG)
Problems with Backus-Naur Form (BNF)
Need meaningContext sensitive
Introduction of First Order LogicBNF First Order LogicS NP VP NP(s1) /\ VP(s2) S(Append(s1 ,s2))Noun stench | … (s=“stench” \/ …) Noun(s)
DCG Notation
Positive: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.
Extending the Notation
Non-terminal symbols can be augmentedA variable can appear on RHSAn arbitrary logical test can appear on RHS
(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)
Digit(sem) sem { 0 sem 9 }Number(sem) Digit(sem)Number(sem) Number(sem1) Digit(sem2) {sem = 10 sem1 + sem2}
First Order LogicDCG
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Overgeneration
Simple grammar can overgenerateEx: “Me smells a stench.”
To fix we must understandCases of English
Nominative - subjective - “I”Accusative - objective - “me”
New Rules
Use of Augmentation
NP(subjective) VP | …Pronoun(case) | Noun | Article NounVP NP(Objective) | …Preposition NP(Objective)I | you | he | she | …me | you | him | her | …
SNP(case)
VPPP
Pronoun(Subjective)Pronoun(Objective)
NPs VP | …Pronouns | Noun | Article NounPronouno | Noun | Article NounVP NPo | …Preposition NPo
I | you | he | she | …me | you | him | her | …
SNPs
Npo
VPPP
Pronouns
Pronouno
Changes needed to handle subjective and objective cases
Verb Subcategorization
Now have slight improvementMust create a sub-categorization list
Believe the smelly wumpus in 2 2 is dead[S]believe
Is smellyis in 2 2is a pit
[Adjective][PP][NP]
is
smell a wumpussmell awfulsmell like a wumpus
[NP][Adjective][PP]
smell
give the gold in 3,3 to megive me the gold
[NP , PP][NP , NP]
give
ExampleSubcatsVerb
Parse TreeS
NP
VP([])
VP([NP])
VP([NP,NP]) NP NP
Pronoun Pronoun Article NounVerb([NP,NP])
You give me the gold
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Semantic InterpretationSemantic Interpretation: Responsible for combining meanings compositionally to get a set of possible interpretationsFormal Languages
Compositional Semantics: The semantics of any phrase is a function of its subphrases
• X + Y
We can handle an infinite grammar with a finite set of rules
Natural LanguagesAppears 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
Semantic InterpretationSemantics as DCG Augmentation
The same idea used to specify the semantics of numbers and 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 sem9 }
Number(sem) –> Digit(sem)
Number(sem) –> Number(sem1) Digit(sem2) { sem = 10 × sem1 + sem2 }
Operator(sem) –> sem { sem +,–,×,÷}}
The Semantics of E1
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))
Pragmatic InterpretationThrough semantic interpretation, an agent can perceive a string of words and use a grammar to derive a set of possible semantic interpretations.
Now we address the problem of completing the interpretation by adding information about the current situation
Information which is noncompositional and context-dependant
Pragmatic InterpretationIndexicals: Phrases that refer directly to the current situation
“I am in Boston today.”
Anaphora: Phrases referring to objects that have been mentioned previously
“John was hungry. He entered a restaurant.”“After John proposed to Marsha, they found a preacher and got married. For the honeymoon, they went to Hawaii.”
Deciding which reference is the right one is a part of disambiguation.
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
Ambiguity and Disambiguation
The biggest problem in communicative exchange is that 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.
Ambiguity
Lexical Ambiguitya word has more than one meaning
Syntactic Ambiguity (Structural Ambiguity)
more than one possible parse for the phrase
Semantic Ambiguityfollows from lexical or syntactic ambiguity
Referential Ambiguitysemantic ambiguity caused by anaphoric expressions
Ambiguity
Pragmatic AmbiguitySpeaker and hearer disagree on what the current situation is.
Local AmbiguityA substring can be parsed several ways.
VaguenessNatural languages are also vague
• “It’s hot outside.”
Disambiguation
Disambiguation is a question of diagnosis.
Models of the world are used to provide possible interpretations of a speech act.
Models of the speakerModels of the hearer
It is difficult to pick the right interpretation because there may be several right ones.
Disambiguation
In general, disambiguation requires the combination of four models:
the world modelthe mental modelthe language modelthe acoustic model
Natural language often uses deliberate ambiguity.
Most language understanding programs ignore this possibility
Disambiguation
Context free grammars do not provide a very useful language 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)
Overview
Communication as ActionTypes of Communicating AgentsA Formal Grammar for a Subset of EnglishSyntactic Analysis (Parsing)Definite Clause Grammar (DCG)Augmenting a GrammarSemantic InterpretationAmbiguity and DisambiguityA Communicating Agent
A Communicating Agent
How does this all fit in to an agent that can communicate?
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.
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
SummaryAgents send signals to each other using a speech act.All animals use some conventional signs to communicate, but humans use language in a more sophisticated way that enables them to communicate much moreFormal language theory and phrase structure grammars are useful tools for dealing with some aspects of natural languageCommunication involves
three steps by the speaker • intention, generation and synthesis
four steps by the hearer • perception, analysis, disambiguation and incorporation
SummaryThe encoded message model of communication says that a speaker encodes a representation of a proposition into language, and the hearer decodes the message to uncover the propositionThe situated language model states that the meaning of a message is a function of both the message and the situation in which it occurs.Augmenting a grammar allows us to handle many problems
Definite Clause Grammar (DCG) is an extension of BNF that allows for augmentations
There are many algorithms for parsing strings.I.e. bottom up, top down, combination, and dynamic
SummaryPragmatic interpretation takes the current situation into account to determine the effect of an utterance in context
Disambiguation is the process of deciding which of the possible interpretations is the one that the speaker intended to convey.
The End
BibliographyNorvig, Peter and Russell, Stuart, 1995. “Artificial Intelligence A Modern Approach”, Prentice-Hall Inc., Upper Saddle River, New Jersey.