Transcript 580-06-Communication

CPE/CSC 580:
Intelligent Agents
Franz J. Kurfess
Computer Science Department
California Polytechnic State University
San Luis Obispo, CA, U.S.A.
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Course Overview
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Introduction
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Intelligent Agent, Multi-Agent Systems
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Agent Examples
Agent Architectures
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Reasoning Agents
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Agent Encounters, Resource Sharing, Agreements
Communication
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Observation, Analysis, Performance Improvement
Multi-Agent Interactions
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Knowledge, Reasoning, Planning
Learning Agents
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Agent Hierarchy, Agent Design Principles
Speech Acts, Agent Communication Languages
Collaboration
© Franz J. Kurfess
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Overview Communication
among Agents
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Motivation
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Objectives
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Communication
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speech acts; agent communication languages
Cooperation
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self-interest, societal benefits
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Important Concepts and Terms
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Chapter Summary
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Motivation
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Objectives
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Communication
Communication Basics
Speech Acts
Language: Syntax, Semantics,
Pragmatics
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Basic Concepts
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communication
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exchange of information
requires a shared system of signs
greatly enhanced by language
speaker
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produces signs as utterances
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general: not only spoken language
listener (hearer)
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perceives and interprets signs
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Communication among Agents
[Woolridge 2009]
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Purpose of Communication
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sharing of information among agents or systems
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query other agents for information
responses to queries
requests or commands
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offer
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proposition for collaboration
acknowledgement
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actions to be performed for another agent
confirmation of requests, offers
sharing
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of experiences, feelings
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Communication Problems
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intention
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timing
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what sign system should be used
interpretation
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which act is the right one
language
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when is a communication act appropriate
selection
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what is the expected outcome (speaker’s perspective)
will the intended meaning be conveyed to the listener
ambiguity
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can the intention be expressed without the possibility of misunderstandings
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Language and
Communication
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Natural Language
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used by humans
evolves over time
moderately to highly ambiguous
Formal Languages
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invented
rigidly defined
little ambiguity
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Natural Language
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formal description is very difficult
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mostly used for human communication
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sometimes non-systematic, inconsistent, ambiguous
easy on humans
tough on computers
context is critical
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situation, beliefs, goals
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Formal Languages
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symbols
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terminal symbols
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finite set of basic words
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not: alphabet, characters
non-terminal symbols
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strings
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intermediate structures composed of terminal or non-terminal
symbols
sequences of symbols
phrases
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sub-strings grouping important parts of a string
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Formal Languages Cont.
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sentences
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grammar
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allowable strings in a language
composed from phrases
rules describing correct sentences
often captured as rewrite rules in BNF notation
lexicon
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list of allowable vocabulary words
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Communication Models
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encoded message model
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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
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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
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telepathic communication
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speaker and listener have a shared internal representation
communication through Tell/Ask directives
language-based communication
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speaker performs actions that produce signs which other agents
can perceive and interpret
communication language is different from the internal
representation
more complex
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involves several mappings
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language needs to be generated, encoded, transmitted, decoded, and
interpreted
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Telepathic Communication
© Franz J. &
Kurfess
[Russell
Norvig 1995]
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Language-Based
Communication
© Franz J. &
Kurfess
[Russell
Norvig 1995]
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Communication Steps:
Speaker
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intention
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generation
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decision about producing a speech act
conversion of the information to be transferred into the chosen
language
synthesis
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actions that produce the generated signs
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Communication Steps:
Listener
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perception
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reception of the signs produced by the speaker
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analysis
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syntactic interpretation (parsing)
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semantic interpretation
disambiguation
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speech recognition, lip reading, character recognition
selection of the most probable intended meaning
incorporation
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the selected interpretation is added to the existing world model as
additional piece of evidence
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Communication Example
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[Russell & Norvig 1995]
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Speech Acts
Basics
Speech Act Theory
Mappings
Components
Semantics
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Speech Act
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used for the production of language
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independent of the communication mode
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word
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basic meaningful communicative sign
smaller entities may exist
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e.g. syllable, phonem, letter
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don’t carry meaning
speaker (sender)
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talking, sign language, typing, flags
producer of an utterance
hearer (listener, recipient)
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consumer of an utterance
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Speech Act Theory
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developed in linguistics, cognitive science,
communication theory
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pragmatic theories of language
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utterances
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based on language use
elementary speech actions
based on or related to intentions
different typologies of speech acts
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Speech Acts - Searle
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Searle (1969) identified various different types of
speech act:
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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
[Woolridge 2009]
8-8
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Speech Act Components
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a performative verb:
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e.g., request, inform, promise, …
propositional content:
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e.g., “the door is closed”
[Woolridge 2009]
8-9
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Speech Act Mappings
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Speech act <=> performatives & content:
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performative = request
content = “the door is closed”
speech act = “please close the door”
performative = inform
content = “the door is closed”
speech act = “the door is closed!”
performative = inquire
content = “the door is closed”
speech act = “is the door closed?”
[Woolridge 2009]
8-10
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Speech Act Semantics
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intention of the speaker
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interpretation by the listener
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leads to a specific formulation of a statement
may be different from the intended meaning
methods from other AI areas have been
applied
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e.g. planning
[Woolridge 2009]
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Agent Communication
Languages
standard formats for the exchange of
knowledge and information
usually based on messages
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KQML
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KQML (Knowledge Query and Manipulation
Language)
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developed by the ARPA knowledge sharing
initiative
KIF (Knowledge Interchange Format)
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designed to work in conjunction with KQML
[Woolridge 2009]
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KQML and KIF
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KQML is an ‘outer’ language
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defines various acceptable ‘communicative verbs’, or
performatives
Example performatives:
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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
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related to knowledge representation languages
[Woolridge 2009]
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KIF – Knowledge Interchange
Format
Used to state:
 Properties of things in a domain
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Relationships between things in a domain
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e.g., “Orna is chairman”
e.g., “Michael is Yael’s boss”
General properties of a domain
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e.g., “All students are registered for at least one
course”
[Woolridge 2009]
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KIF Examples
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“The temperature of m1 is 83 Celsius”:
(= (temperature m1) (scalar 83 Celsius))
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“An object is a bachelor if the object is a man
and is not married”:
(defrelation bachelor (?x) :=
(and (man ?x) (not (married ?x))))
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“Any individual with the property of being a
person also has the property of being a
mammal”:
(defrelation person (?x) :=> (mammal ?x))
[Woolridge 2009]
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KQML and KIF
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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
[Woolridge 2009]
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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))
[Woolridge 2009]
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Criticisms of KQML
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fluid performative set
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transport mechanisms not precisely defined
semantics not rigorously defined
missing commissives
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leading to interoperability problems
performatives for making commitments
performative set too large and ad hoc
[Woolridge 2009]
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FIPA Agent Communication Language
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program of agent standards
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initiated by the Foundation for Intelligent Physical
Agents (FIPA)
the centerpiece is an ACL
structure similar to KQML
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performatives
20 performatives in FIPA
content
the actual content of the message
housekeeping
e.g., sender, receiver, ...
[Woolridge 2009]
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FIPA ACL Example
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Example:
(inform
:sender
:receiver
:content
:language
:ontology
)
agent1
agent5
(price good200 150)
sl
hpl-auction
[Woolridge 2009]
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FIPA Performatives
[Woolridge 2009]
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“Inform” and “Request”
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two basic performatives in FIPA
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all others are macro definitions
defined in terms of “Inform” and “Request”.
semantics of “Inform” and “Request”
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pre-condition
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what must be true in order for the speech act to
succeed
“rational effect”
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what the sender of the message hopes to bring about
[Woolridge 2009]
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“Inform”
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pre-condition is that the sender
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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
[Woolridge 2009]
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“Request”
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pre-condition is that the sender:
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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
[Woolridge 2009]
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Summary Communication
© Franz J. Kurfess
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Important Concepts and
Terms
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agent
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Agent Communication Language
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alphabet
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ambiguity
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communication
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collaboration
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coordination
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formal language
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grammar
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hearer
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KIF
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KQML
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language
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lexicon
© Franz J. Kurfess
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