agent communication michael floyd sysc 5103 – software agents november 13, 2008

Agent Communication

Michael Floyd

SYSC 5103 – Software AgentsNovember 13, 2008

November 13,2008mfloyd@sce.carleton.ca Slide 2

Outline

• Speech Acts

• Shared Ontology

• Agent Communication Language

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Speech Acts

• Speech act theory: communication is an action

• Action attempts to influence environment (other agents)

• No guarantee of success, just like any other action

• Not the same master-slave relation as in programming -> a.method(message)

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Theory of Speech Acts

• Speech changes the state of the world

– “I now pronounce you man and wife”

– “The meeting is at noon”

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Aspects of Speech Acts

• Locutionary act – the act of uttering the words

• “Please make me some tea.”

• Illocutionary act – what is done in saying the words

• A request for tea to be made

• Perlocution act – what is done by saying the words

• Someone made you tea

November 13,2008mfloyd@sce.carleton.ca Slide 6

Aspects of Speech Acts (2)

• The hearer must:

– Parse the message

– Infer the same meaning as the sender

• “Could you pass me the salt?”

– Willfully want to perform the action

• Is doing this in line with my goals or even possible?

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Classes of Speech Acts (Searle)

• Representatives– try and get the hearer to believe something (claim, insist, etc.)

• Directives– a command to attempt to get the hearer to do something

(request, forbid, etc.)

• Commissives– commit the speaker to a course of action (promise, vow, etc.)

• Expressives– express a psychological state (thank, congratulate, etc.)

• Declaratives– Declare a change in the world (wed, baptize, define, etc.)

November 13,2008mfloyd@sce.carleton.ca Slide 8

Speech Acts in a Plan

Request(Speaker, Hearer, act)

Preconditions: • Speaker believes Hearer can perform act or Speaker believes

Hearer believes it can perform act

• Speaker believes it wants act to be performed

• Speaker believes Hearer wants act to be performed

Effect: • Speaker believes Hearer wants to perform act

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Shared Ontology

• The communicating agent should agree to a terminology

• Allows the agents to communicate in a consistent manner

• For example, is a bat a baseball bat or an animal bat?

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Agent Communication Languages

• Standardized and structured languages for agents to communicate with each other

• Examples:– KQML– FIPA– COOL– Boissier/Demazeau's Interaction Language – CMIP

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Knowledge Sharing Effort (KSE)

• Two main deliverables from this project– Knowledge Interchange Format (KIF)

• content of the message

– Knowledge Query and Manipulation Language (KQML) • the illocutionary act of the message

• with the content in KIF

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KIF

• Uses logic to define:– Properties of things

• Tom is a vegetarian

– Relationships between things• Tom and Janine are married

– Properties of the domains• Everyone has a mother

November 13,2008mfloyd@sce.carleton.ca Slide 13

KIF Examples

(= (temperature m1) (scalar 83 Celsius))

The temperature, m1, is a scalar equal to 83 Celsius.

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KIF Examples (2)

(defrelation bachelor (?x) := (and (man ?x) (not (married ?x))))

?x is a variable and if ?x is a man and not married, then ?x is a bachelor

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KIF Example (3)

(defrelation person (?x) :=> (mammal ?x))

If ?x is a person it is also a mammal.

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KQML

• A message between agents

• Each message has a performative and a number of parameters

• Used as an “envelop” around content (like KIF)

From: A Proposal for a new KQML Specification

By:Yannis Labrou and Tim Finin.

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KQML Parameters

:sender sender of the message

:receiver intended recipient

:content content of the message

:language the language of the content

:ontology the terminology of the message

:reply-with identifier for the reply (if one is needed)

:in-reply-to reference to the reply-with

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Example #1 – Initial Message

(ask-one

:sender trader-agent

:receiver stock-server

:language LPROLOG

:ontology NYSE-TICKS

:reply-with q1

:content (PRICE IBM ?price)

)

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Example #1 - Response

(tell

:sender stock-server

:receiver trader-agent

:language LPROLOG

:ontology NYSE-TICKS

:in-reply-to q1

:content (PRICE IBM 14)

)

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Example #2 – Initial Message

(stream-about

:sender A

:receiver B

:language KIF

:ontology motors

:reply-with q2

:content m1

)

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Example #2 – Responses (1)

(tell

:sender B

:receiver A

:language KIF

:ontology motors

:in-reply-to q2

:content (= (torque m1) (scalar 12 kgf))

)

November 13,2008mfloyd@sce.carleton.ca Slide 23

Example #2 – Responses (2)

(tell

:sender B

:receiver A

:language KIF

:ontology motors

:in-reply-to q2

:content (= (status m1) normal))

November 13,2008mfloyd@sce.carleton.ca Slide 24

Example #2 – Responses (3)

(eos:sender B

:receiver A

:in-reply-to q2

)

Tells agent A that the stream of responses is done.

November 13,2008mfloyd@sce.carleton.ca Slide 25

Criticism of KQML

• No guarantee different implementations would interoperate

• Performatives had meanings defined using english, so open to interpretation

• No commissive performatives

• The performatives set was overly large

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Foundation for Intelligent Physical Agents

• FIPA ACL was a an attempt to address shortcomings of KQML

• FIPA ACL messages are very similar to KQML messages

(inform:sender agen1

:receiver agent2

:content (price good2 150)

:language s1

:ontology hpl-auction

)

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FIPA

• Aims for more formal message semantics

• Semantics provided in a formal language : SL

• SL allows the representation of beliefs, desires and uncertain beliefs

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FIPA (2)

<i, inform(j, φ)>

feasibility precondition: Biφ ۸ ¬B

i(Bif

jφ ٧ Uif

jφ )

rational effect: Bjφ

Pre: Agent i believe φ and does not believe that j has a firm belief about φ or is uncertain about φ

Post: Agent j should believe φ (hopefully)

November 13,2008mfloyd@sce.carleton.ca Slide 29

References

• Chapter 8 of “An Introduction to Multiagent Systems”, Michael Wooldridge