Agent Communications

• Necessity

• Communication languages

• Communication architectures

Motivation for Agent Communication

”Language is a very difficult thing to put into words” – Voltaire

1. Communication is required for cooperation between agents

2. Societies can perform tasks no individual agent can

3. Communicating agents need only know a ”common language”

4. Supports heterogenous agents

The nature of communication

Human communication Communication is the intentional exchange of information brought

about by the production and perception of signs drawn from a shared system of conventional signs (AIMA, Russell&Norvig) language

Communication seen as an action (communicative act) and as an intentional stance

Component steps of communicationSpeaker Hearer Intention Perception Generation Analysis Synthesis Disambiguation

Incorporation

3

SyntaxSemanticsPragmatics

The environment provides a computational infrastructure where interactions among agents take place. The infrastructure includes protocols for agents to communicate and protocols for agents to interact

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Artificial Communicationin a multi-agents system

ACL

• Agent Communication Language (ACL) is based on

speech-act theory .

• Speech Acts

...speaking a language is performing speech acts, acts such

as making statements, giving commands, asking questions,

making promises, and so on. - John Searle

Speech Acts

• Speech act theories are pragmatic theories of language, i.e., theories of language use: they attempt to account for how language is used by people every day to achieve their goals and intentions

• The origin of speech act theories are usually traced to Austin’s 1962 book, How to Do Things with Words

Theory of Speech ActsJ. Austin - How to do things with words, 1962, J. Searle - Speech acts, 1969

A speech act has 3 aspects: locution = physical utterance( 発話 ) by the speaker illocution = the intended meaning of the utterance by the speaker (performative) prelocution = the action that results from the locution

Alice told Tom: "Would you please close the door"locution illocution contentprelocution: door closed (hopefully!)

Illocutionary aspect - several categories Assertives, which inform: the door is shut Directives, which request: shut the door, can pelicans fly? Commissives, which promise something: I will shut the door Permissive, which gives permission for an act: you may shut the door Prohibitives, which ban some act: do not shut the door Declaratives, which causes events: I name you king of Ruritania Expressives, which express emotions and evaluations: I am happy

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An utterance is a spoken word or string of spoken words. At the simplest level, to utter is simply to say a word with no particular forethought or intention to communicate a meaning.

Propositional Utterance is a more meaningful type of utterance makes reference to or describes a real or imaginary object.

An illocutionary utterance is spoken with the intention of providing information, soliciting answers to questions, giving praise, and so on

Perlocutionary utterances, on the other hand, do attempt to effect a change.

The Speech Act Model

ACLs – communication as action - communicative acts - standard formats for the exchange of messages

KQML and KIF

• The best known ACL is KQML, developed by the ARPA knowledge sharing initiativeKQML is comprised of two parts:– the knowledge query and manipulation language

(KQML)– the knowledge interchange format (KIF)

KQML

• KQML is an ‘outer’ language, that 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 . . . ’)

Categories of KQML performatives

1. Basic Query performatives

2. Multi-response query performatives

3. Response performatives

4. Generic Informational performatives

5. Generator performatives

6. Capability performatives

7. Networking performatives

(ask-one :sender joe:receiver ibm-stock:reply-with ibm-stock:language PROLOG:ontology NYSE-TICKS:content (price ibm ?price) )

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(tell :sender willie :receiver joe :reply-with block1 :language KIF :ontology BlockWorld :content (AND (Block A)(Block B)

(On A B)) )

1. Query performatives:ask-one, ask-all, ask-if, stream-all,...

(stream-all :sender willie:receiver ibm-stock

:content (price ?VL ?price ) )(standby

:content (stream-all:content (price ?VL ?price) )

ask-one(P)

tell(P)

tell(P1)

stream-all(P)

tell(P2)eos

tell(P1,P2,...)

ask-all(P)

B B B

A

A

A

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4. Generic informational performatives:tell, untell, insert, delete, ...

In fact, KQML contains only 2 types of illocutionary acts: assertives and directives

+ facilitator and network-related performatives (no necessarily speech acts)

tell(P)

untell(P)

delete(P)

insert(P)

2. Generator performatives:standby, ready, next, rest, discard, generate,...

6. Network performatives:register, unregister, forward, route, ...

3. Response performatives:reply, sorry ...

5. Capability performatives:advartise, subscribe, recommend...

Facilitator

A

A

B

B

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Facilitator agent= an agent that performs various useful communication services:

maintaining a registry of service names (Agent Name Server) forwarding messages to named services routing messages based on content matchmaking between information providers and clients providing mediation and translation services

tell(P)

ask(P)

subscribe(ask(P)) tell(P)

tell(P)

advertise(ask(P))

tell(P)

recruit(ask(P))

ask(P)

recommend(ask(P)) advertise(ask(P))

tell(P)

ask(P)

reply(B)

A

A

A

A

B

B

B

B

KQML Examples I

AB - (tell (> 3 2))

AB - (perform (print ”hello” t))BA – (reply done)

AB - (ask-if (> (size chip1) (size chip2) ))BA – (reply true)

AB - (subscribe (position ?x ?r ?c))BA – (tell (position chip1 8 10))BA – (tell (position chip2 8 46))BA – (tell (position chip3 3 64))AB - (unsubscribe (position ?x ?r ?c))

(ask-one :content (geoloc TRD (?long ?lat))

:ontology geo-model3)

(ask-all

:content ”price(IBM, [?price, ?time])”

:receiver stock-server

:language standard-prolog

:ontology NYSE-TICS)

KQML Examples II

KIF – Knowledge Interchange Format

KIF is a language for expressing message content Used to state:• Properties of things in a domain (e.g., “Noam

is chairman”)• Relationships between things in a domain

(e.g., “Amnon is Yael’s boss”)• General properties of a domain (e.g., “All

students are registered for at least one course”)

KIF examples - I

Terms:(size chip1)

(+ (sin theta)(cos theta))

(if (> theta 0) theta (-theta))

(setofall ?x (above ?x chip1))

Sentences:(Prime 565762761)

(> (sin theta) (cos phi))

(not (> (sin theta) 0)))

(> (* (width chip1) (length chip2))(*(width chip1)(length chip2)))

(=> (> ?x 0) (positive ?x))

KIF Examples - II

Definitions:(defrelation leq(?x ?y) := (not (> ?x ?y)))

(defrelation natural(?x) := (and (integer ?x) (>= ?x 0)))

Procedures:(progn (fresh_line t)(print ”Hi!”)(fresh_line t))

Meta-Knowledge:(believes John ’(material moon jarlsberg))

(=> (believes John ?p) (believes Mary ?p))

Rules:(<<= (flies ?x)(bird ?x))

KQML Statement Structure• KQML Statements consists of

1. A performative

2. Parameters and context information

General syntax:

(KQML-performative

:sender word

:receiver word

:language word

:ontology word

:content expression

...)

• A formal specification of a set of terms is known as an ontology• The knowledge sharing effort has associated with it a large effort at defining common ontologies 　 - software tools like ontolingua

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OntologiesOntology = a specification of objects, concepts, and

reationships in a particular domain; it comprises a vocabulary, a domain theory and a conceptual schemata to describe organization and interpretation

An ontology is more than a taxonomy of classes,it must also describe relationships

x (Block x) (PhysicalObject x)Instead of (Block A)

(InstanceOf A Block)

(Class Block) Hierarchy

(Class PhysicalObjects)

(SubclassOf Block PhysicalObjects)

x,y,z (InstanceOf x y) (SubclassOf y z)

(InstanceOf x z)Ontology editors frame-based KR systems that allow the user to define an ontology and its components: classes, instances, relationships, and functions

Person

PupilStudEmpl

Sun_EIBM_E

Person

Empl

Woman

Stud

Man

Joe Alice

Joe Alice

KQML Agent naming

• System for mapping agents into names is important in most ACLs

• KQML assumes that names are local – A can register with B under the name Alice– A can register with C under the name Albert

• Doesn’t preclude the use of a central Agent Name Server, an architecture used by most systems

• What gets registered under a name? Contact information like:

name(amundbot, tcpip, [cavenan.idi.ntnu.no,80]).name(amundbot,smtp,[amundbot@jfipa.org)name(amundbot,http,[www.jfipa.org:80/])

Facilitators - I

Agents performing various (useful) communication services

1. Maintain registry of service names

2. Forward messages to named services

3. Route messages based on content

4. Provide ”matchmaking”

5. Provide mediation and translation services

Routers

• Content-independent message routers

• Each KQML-agent is associated with its own separate router process

• Router handles all outgoing/incoming ACL messages

• Outgoing messages can specify a particular agent address (to agent or router)

• Message can specify a description of context

• Delivery of messages is not guaranteed

Other ACLs

• Telescript – supports mobile computing

• FIPA ACL – competing/extending KQML

• FIPA vs KQML– Both are based on speech act

– Different set of performatives

– FIPA has a more formal basis

– FIPA can describe interaction protocols

– FIPA is probably becoming the standard ACL

• More recently, the Foundation for Intelligent Physical Agents (FIPA) started work on a program of agent standards — the centerpiece is an ACL

• Basic structure is quite similar to KQML:– performative

20 performative in FIPA

– housekeepinge.g., sender, etc.

– contentthe actual content of the message

FIPA’s Agent Communication Language Specifications

FIPA Example

(inform:sender agent1:receiver agent5:content (price good200 150):language sl:ontology hpl-auction

)

FIPA

“Inform” and “Request”• “Inform” and “Request” are the two basic

performatives in FIPA. All others are macro definitions, defined in terms of these.

• The meaning of inform and request is defined in two parts:– 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

“Inform”

• For the “inform” performative…The content is a statement.Pre-condition is that 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

“Request”

• For the “request” performative…The content is an action.Pre-condition is that 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

What is FIPA?

• The Foundation for Intelligent Physical Agents (FIPA) is a non-profit association.

• FIPA’s purpose is to promote the success of emerging agent-based applications, services and equipment.

• FIPA’s goal is pursued by making available in a timely manner, internationally agreed specifications that maximise interoperability across agent-based applications, services and equipment.

• http://www.fipa.org/

Who is FIPA?

• FIPA operates through the open international collaboration of member organisations, which are companies and universities active in the agent field.

• Companies: Alcatel, Boeing, British Telecom, Deutsche Telekom, France Telecom, Fujitsu, Hitatchi, HP, IBM, Fujitsu, Hewlett Packard, IBM, Intel, Lucent, NEC, NHK, NTT, Nortel, Siemens, SUN, Telia, Toshiba, etc.

• Universities and Research Institutes: GMD, EPFL, Imperial, IRST, etc.

• Government Agencies: DARPA

FIPA Encodings and package

Fipa supports three main types of syntax encoding:

1. Extensible Markup Language – XML

2. Proprietary Binary format

3. Lisp-like format

• Separates between Envelopes and Messages

Example - XML-encoded FIPA ACL

1. <?xml version="1.0"?>2. <envelope>3.   <params index="1">4.     <to>5.       <agent-identifier>6.         <name>receiver@foo.com</name>7.         <addresses>8.           <url>http://foo.com/acc</url>9.         </addresses>10.       </agent-identifier>11.     </to>12.     <from>13.       <agent-identifier>14.         <name>sender@bar.com</name>15.         <addresses>16.           <url>http://bar.com/acc</url>17.         </addresses>18.       </agent-identifier>19.     </from>20.  21.     <acl-representation>fipa.acl.rep.xml.std</acl-representation>22.  23.     <date>20000508T042651481</date>24.  25.     <encrypted>no encryption</encrypted>26.  27.     <received >28.       <received-by value="http://foo.com/acc" />29.       <received-date value="20000508T042651481" />30.       <received-id value="123456789" />31.     </received>32.   </params>33. </envelope>34.  

Binary encoded FIPA XML

1. 0xfe 0x00 0x97 0x12 0x20 0x31 0x11 0x06 0x19 0x15 0x37 0x62 0x59 0x20 0x02 0x03 0x02

2. ‘r’  ‘e’  ‘c’  ‘e’  ‘i’  ‘v’  ‘e’  ‘r’  ‘@’  ‘f’  ‘o’  ‘o’  ‘.’  ‘c’  ‘o’  ‘m’  0x00

3. 0x02 ‘h’  ‘t’  ‘t’  ‘p’  ‘:’  ‘/’  ‘/’  ‘f’  ‘o’  ‘o’  ‘.’  ‘c’  ‘o’  ‘m’  ‘/’  ‘a’ 

4. ‘c’  ‘c’  0x00 0x01 0x01 0x02 ‘s’  ‘e’  ‘n’  ‘d’  ‘e’  ‘r’  ‘@’  ‘b’  ‘a’  ‘r’  ‘.’ 

5. ‘c’  ‘o’  ‘m’  0x00 0x02 ‘h’  ‘t’  ‘t’  ‘p’  ‘:’  ‘/’  ‘/’  ‘b’  ‘a’  ‘r’  ‘.’  ‘c’ 

6. ‘o’  ‘m’  ‘/’  ‘a’  ‘c’  ‘c’  0x00 0x01 0x01 0x08 ‘n’  ‘o’  ‘ ’  ‘e’  ‘n’  ‘c’  ‘r’ 

7. ‘y’  ‘p’  ‘t’  ‘i’  ‘o’  ‘n’  0x00 0x0a ‘h’  ‘t’  ‘t’  ‘p’  ‘:’  ‘/’  ‘/’  ‘b’  ‘a’ 

8. ‘r’  ‘.’  ‘c’  ‘o’  ‘m’  ‘/’  ‘a’  ‘c’  ‘c’  0x00 0x20 0x31 0x11 0x06 0x19 0x15 0x37

9. 0x62 0x59 0x20 0x03 ‘1’  ‘2’  ‘3’  ‘4’  ‘5’  ‘6’  ‘7’  ‘8’  ‘9’  0x00 0x01

10.  

Shortcomings of current ACLs

• Intentional level description: which mental attitudes, what definitions?

• Problems with mental attitudes: from theory to practice

• Can all desirable communication primitives be modeled after speech acts? Should they?

• Flexible description of agents’ capabilities and advertising of such capabilities.

• How can we test an agent’s compliance with the ACL?

• Ease of extending an ACL

Conclusions of Current ACLs

• Agent Communication Languages have a common basis – speech act

• Syntax is well specified, but current research is on describing semantics

Motivation for KIF(Knowledge Interchange Format)

• Creating language for development of intelligent applications

• Creating language for common interchange format

Note:

• KIF is not intended for interaction with humans

• KIF is not intended to be internal representation for knowledge within computer programs

http://logic.stanford.edu/kif/dpans.html

KIF Features

1. Prefix version of 1st order predicate calculus (logic)

2. Declarative semantics

3. Logically comprehensive

4. Provides representation of knowledge about representation of knowledge

Additional features:

• Translatability

• Readability

• Usability

KIF General Overview

Variables:

• ?singlevar, @sequence

Operators:Term Operators: listof, if, ..

Sentence Operators: not, and, /=, ...

Rule Operators: =>>, ..

Definition Operators: defobject, deffunction

Constants:

object, function, relational, logical

Expressions:Word or a finite sequence of words (i.e. Sentences)

Agent Vocabularies

• Agents should use words consistently

Open-ended Dictionary

• Each word has:– English description for understanding by humans

– KIF (or alternative) for understanding by computers

• Dictionary would contain multiple ontologies for many areas

Ontology Inference Layer – OILhttp://www.ontoknowledge.org/oil/

• OIL is used to specify and exchange ontologies

• Three roots of OIL:1. Description Logics

2. Frame-based Systems

3. Web-standards: XML and RDF

• Small, not too expressive (as possibly the case with Ontolingua)

OIL Example

ontology-container:title: ”african animals”

subject: ”animal, food, vegetarians”

description: ”example ontology describing african animals”

Language ”en-uk”

Source http://www.url.com/

ontology-definitions:slot-def: eats

inverse: is-eaten-by

class-def: animal

class-def: plant

Terminology of Agent Communication

Speech Act – Formal subset of natural language representing actions

ACL – Agent Communication Language

FIPA - Foundation for Intelligent Physical Agents

KQML – Knowledge Query and Manipulation Language

Ontology – ”World Model”, formal description of agent domain

Encoding – syntactic representation of ACL messages

ACC – Agent Communication Channel (FIPA)

KSE – Knowledge Sharing Effort

KIF – Knowledge Interchange Format

Router – entity that sends incoming messages in correct ”direction”

Facilitator – An agent that includes a Router

Semantics on the Web - terminology

Semantic WebRDF – Resource Decription FrameworkOIL – Open Inference LayerXML/XML Schema OntolinguaOKBC – Open Knowledge Base ConnectivityDAML – DARPA Agent Markup LanguageDAML-S – Service description language based on DAMLUDDI – Universal Description, Discovery and IntegrationWSDL – Web Services Description LanguageSHOE – Simple HTML Ontology ExtensionsebXML – e-business XML

Exercise

• Read the paper: kqml-acl.pdf

Present your understanding of the paper in 10-15 minutes in next lecture.