1 Computer Science Department California Polytechnic State University San Luis Obispo, CA, U.S.A. Franz J. Kurfess CPE/CSC 580: Intelligent Agents 1
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Computer Science DepartmentCalifornia Polytechnic State University
San Luis Obispo, CA, U.S.A.
Franz J. Kurfess
CPE/CSC 580: Intelligent Agents
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Course Overview❖ Introduction
Intelligent Agent, Multi-Agent Systems Agent Examples
❖ Agent Architectures Agent Hierarchy, Agent Design Principles
❖ Reasoning Agents Knowledge, Reasoning, Planning
❖ Learning Agents Observation, Analysis, Performance Improvement
❖ Multi-Agent Interactions Agent Encounters, Resource Sharing, Agreements
❖ Communication Speech Acts, Agent Communication Languages
❖ Collaboration Distributed Problem Solving, Task and Result Sharing
❖ Agent Applications Information Gathering, Workflow, Human Interaction, E-Commerce, Embodied Agents, Virtual Environments
❖ Conclusions and Outlook
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Overview Communication among Agents
❖ Motivation
❖ Objectives
❖ Communication speech acts; agent communication languages
❖ Cooperation self-interest, societal benefits
❖ Important Concepts and Terms
❖ Chapter Summary
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Basic Concepts
❖ communication exchange of information requires a shared system of signs greatly enhanced by language speaker
produces signs as utterances general: not only spoken language
listener (hearer) perceives and interprets signs
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Purpose of Communication
❖ sharing of information among agents or systems query other agents for information responses to queries requests or commands
actions to be performed for another agent offer
proposition for collaboration acknowledgement
confirmation of requests, offers sharing
of experiences, feelings
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Communication Problems
❖ intention what is the expected outcome (speaker’s perspective)
❖ timing when is a communication act appropriate
❖ selection which act is the right one
❖ language what sign system should be used
❖ interpretation will the intended meaning be conveyed to the listener
❖ ambiguity can the intention be expressed without the possibility of misunderstandings
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Language and Communication
❖ Natural Language used by humans evolves over time moderately to highly ambiguous
❖ Formal Languages invented rigidly defined little ambiguity
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Natural Language
❖ formal description is very difficult sometimes non-systematic, inconsistent, ambiguous
❖ mostly used for human communication easy on humans tough on computers
❖ context is critical situation, beliefs, goals
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Formal Languages
❖ symbols terminal symbols
finite set of basic words not: alphabet, characters
non-terminal symbols intermediate structures composed of terminal or non-
terminal symbols
❖ strings sequences of symbols
❖ phrases sub-strings grouping important parts of a string
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Formal Languages Cont.
❖ sentences allowable strings in a language composed from phrases
❖ grammar rules describing correct sentences often captured as rewrite rules in BNF notation
❖ lexicon list of allowable vocabulary words
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Communication Models
❖ encoded message model a definite proposition of the speaker is encoded into
signs which are transmitted to the listener the listener tries to decode the signs to retrieve the
original proposition errors are consequences of transmission problems
❖ situated language model the intended meaning of a message depends on the
signals as well as the situation in which they are exchanged
mis-interpretation may lead to additional problems
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Communication Types
❖ telepathic communication speaker and listener have a shared internal
representation communication through Tell/Ask directives
❖ language-based communication speaker performs actions that produce signs which other
agents can perceive and interpret communication language is different from the internal
representation more complex
involves several mappings language needs to be generated, encoded, transmitted, decoded,
and interpreted
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Communication Steps: Speaker
❖ intention decision about producing a speech act
❖ generation conversion of the information to be transferred into the
chosen language
❖ synthesis actions that produce the generated signs
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Communication Steps: Listener
❖ perception reception of the signs produced by the speaker
speech recognition, lip reading, character recognition analysis
syntactic interpretation (parsing) semantic interpretation
disambiguation selection of the most probable intended meaning
incorporation the selected interpretation is added to the existing world
model as additional piece of evidence
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Speech Act
❖ used for the production of language
❖ independent of the communication mode talking, sign language, typing, flags
❖ word basic meaningful communicative sign smaller entities may exist
e.g. syllable, phonem, letter don’t carry meaning
❖ speaker (sender) producer of an utterance
❖ hearer (listener, recipient) consumer of an utterance
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Speech Act Theory
❖ developed in linguistics, cognitive science, communication theory
❖ pragmatic theories of language based on language use
❖ utterances elementary speech actions based on or related to intentions
❖ different typologies of speech acts
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[Woolridge 2009] 8-8
Speech Acts - Searle Searle (1969) identified various different types of
speech act: representatives:
such as informing, e.g., ‘It is raining’ directives:
attempts to get the hearer to do something e.g., ‘please make the tea’
commissives:which commit the speaker to doing something, e.g., ‘I promise to… ’
expressives:whereby a speaker expresses a mental state, e.g., ‘thank you!’
declarations:such as declaring war or christening
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[Woolridge 2009] 8-9
Speech Act Components
a performative verb: e.g., request, inform, promise, …
propositional content: e.g., “the door is closed”
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[Woolridge 2009] 8-10
Speech Act Mappings Speech act <=> performatives & content:
performative = requestcontent = “the door is closed”speech act = “please close the door”
performative = informcontent = “the door is closed”speech act = “the door is closed!”
performative = inquirecontent = “the door is closed”speech act = “is the door closed?”
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[Woolridge 2009]
Speech Act Semantics
intention of the speaker leads to a specific formulation of a statement
interpretation by the listener may be different from the intended meaning
methods from other AI areas have been applied e.g. planning
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Agent Communication
Languages
standard formats for the exchange of knowledge and information
usually based on messages
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[Woolridge 2009]
KQML KQML (Knowledge Query and Manipulation
Language) developed by the ARPA knowledge sharing
initiative KIF (Knowledge Interchange Format)
designed to work in conjunction with KQML
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[Woolridge 2009]
KQML and KIF KQML is an ‘outer’ language
defines various acceptable ‘communicative verbs’, or performativesExample performatives: ask-if (‘is it true that. . . ’) perform (‘please perform the following action. . . ’) tell (‘it is true that. . . ’) reply (‘the answer is . . . ’)
KIF is a language for expressing message content related to knowledge representation languages
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[Woolridge 2009]
KIF – Knowledge Interchange Format Used to state: Properties of things in a domain
e.g., “Orna is chairman” Relationships between things in a domain
e.g., “Michael is Yael’s boss” General properties of a domain
e.g., “All students are registered for at least one course”
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[Woolridge 2009]
KIF Examples “The temperature of m1 is 83 Celsius”:(= (temperature m1) (scalar 83 Celsius))
“An object is a bachelor if the object is a man and is not married”:(defrelation bachelor (?x) :=
(and (man ?x) (not (married ?x))))
“Any individual with the property of being a person also has the property of being a mammal”:(defrelation person (?x) :=> (mammal ?x))
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[Woolridge 2009]
KQML and KIF communication between agents requires a common
set of terms ontology
formal specification of a set of terms knowledge sharing
requires defining common ontologies OWL - Web Ontology Language ontology editors
Protégé
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[Woolridge 2009]
KQML/KIF Dialogue Example
A to B: (ask-if (> (size chip1) (size chip2)))
B to A: (reply true)
B to A: (inform (= (size chip1) 20))
B to A: (inform (= (size chip2) 18))
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[Woolridge 2009]
Criticisms of KQML fluid performative set
leading to interoperability problems transport mechanisms not precisely defined semantics not rigorously defined missing commissives
performatives for making commitments performative set too large and ad hoc
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[Woolridge 2009]
FIPA Agent Communication Language program of agent standards
initiated by the Foundation for Intelligent Physical Agents (FIPA)
the centerpiece is an ACL structure similar to KQML
performatives20 performatives in FIPA
contentthe actual content of the message
housekeepinge.g., sender, receiver, ...
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[Woolridge 2009]
FIPA ACL Example
Example:(inform
:sender agent1:receiver agent5:content (price good200
150):language sl:ontology hpl-auction
)
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[Woolridge 2009]
“Inform” and “Request”
two basic performatives in FIPA all others are macro definitions defined in terms of “Inform” and “Request”.
semantics of “Inform” and “Request” pre-condition
what must be true in order for the speech act to succeed “rational effect”
what the sender of the message hopes to bring about
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[Woolridge 2009]
“Inform”
pre-condition is that the sender holds that the content is true intends that the recipient believe the content does not already believe that the recipient is
aware of whether content is true or not content is a statement
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[Woolridge 2009] 8-24
“Request”
pre-condition is that the sender: intends action content to be performed believes recipient is capable of performing this
action does not believe that receiver already intends to
perform action content is an action
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Important Concepts and Terms
❖ agent
❖ Agent Communication Language
❖ alphabet
❖ ambiguity
❖ communication
❖ collaboration
❖ coordination
❖ formal language
❖ grammar
❖ hearer
❖ KIF
❖ KQML
❖ language
❖ lexicon
❖ listener
❖ multi-agent system
❖ natural language
❖ pragmatics
❖ recipient
❖ semantics
❖ sender
❖ sign
❖ speech act
❖ syntax
❖ utterance
❖ vocabulary