Agents That Communicate Chris Bourne Chris Christen Bryan Hryciw - PowerPoint PPT Presentation

Agents That Communicate Chris Bourne Chris Christen Bryan Hryciw

Overview Communication 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 Summary

Introduction Communication 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)

Introduction Humans 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 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

Communication as Action Speech 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

Communication as Action Transferring I nformation to Hearer: I nform: 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 Action Make 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 Communication Speaking: 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 Communication Three steps take place in the speaker: I ntention: 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 W 1 (ideally, W = W 1 ) Analysis: H infers that W 1 has possible meanings P 1 , … , P n Disambiguation: H infers that S intended to convey P i (ideally, P i = P) I ncorporation: H decides to believe P i (or rejects it if it is out of line with what H already believes)

Models of Communication Encoded 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 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

Types of Communicating Agents Communicating 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

Tell and Ask Communication with Tell and Ask Agent A Agent B KB KB Percepts Actions Percepts Actions Reasoning Reasoning TELL( KB B , “ P ”) TELL( KB A , “ P ”) TELL( KB B , “ Pit ( P A1 ) ∧ At ( P A1 ,[2,3], S A9 )”) ASK( KB B , “ Q ”)

Formal Language Language Language Agent A Agent B KB KB Percepts Actions Percepts Actions Reasoning Reasoning

Overview Communication 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

Formal Grammar for a Subset of English Lexicon: 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 Grammar: S -> NP VP S -> S Conjunction S NP -> Pronoun VP -> Verb -> Noun -> VP NP -> Article Noun -> VP Adjective -> Digit Digit -> VP PP -> NP PP -> VP Adverb -> NP RelClause RelClause -> that VP PP -> Preposition NP

Overview Communication 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

Parsing Algorithms There 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

Bottom-up Parse (example) forest subsequence rule Article → the The wumpus is dead The Noun → wumpus Article wumpus is dead wumpus NP → Article Noun Article Noun is dead Article Noun Verb → is NP is dead is Adjective → dead NP Verb dead dead VP → Verb NP Verb Adjective Verb VP → Verb Adjective NP VP Adjective VP Adjective S → NP VP NP VP NP VP S 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

Overview Communication 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

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(s 1 ) /\ VP(s 2 ) ⇒ S(Append(s 1 ,s 2 )) Noun → stench | … (s=“stench” \/ …) ⇒ Noun(s)