Lectures
AIProgramming:
IntroductiontoRoboRescue
3AgentsandAgents
4Multi-AgentsandCommunication
5MultiagentDecision
6CooperationAndCoordination
7CooperationAndCoordination
8Machine
9Knowledge
10PuttingItAll
1
2
TDDD10AIProgramming
Multi-AgentsandCommunication
CyrilleBerger
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Lecturegoals
Lecturecontent
Acquireknowledgeonmutliagent
systems.
Acquireknowledgeonhowagents
communicate
Multi-Agent
CMUCaseStudy
Communication
KQML
FoundationforIntelligentPhysicalAgents
(FIPA)
ContractNet
JADE
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Multi-AgentSystems
Multi-AgentSystems
“Amulti-agentsystem(MAS)canbe
definedasalooselycoupled
networkofproblemsolversthat
interacttosolveproblemsthatare
beyondtheindividualcapabilitiesor
knowledgeofeachproblemsolver.”
DurfeeandLesser,1989
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CharacteristicsofMulti-AgentSystems
ViewofacanonicalMulti-AgentSystem
Theparticipantsareself-interested.
Theparticipantsandtheircapabilities
changesovertime,i.e.opensystems.
Eachparticipanthasincomplete
informationorcapabilitiesforsolvingthe
problemand,thus,hasalimited
viewpoint.
Thereisnosystemglobalcontrol.
Dataisdecentralized.
Computationisasynchronous.
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Motivation
Challenges
Howtoformulate,describe,decompose,and
allocateproblemsandsynthesizeresultsamonga
groupofagents.
Howtoenableagentstocommunicateandinteract.
Howtomakesurethatagentsactcoherentlyin
makingdecisionortakingaction.
Howtoenableindividualagentstorepresentand
reasonabouttheactions,plans,andknowledgeof
otheragentstocoordinatewiththem.
Howtorecognizeandreconciledisparate
viewpointsandconflictingintentionsamonga
collectionofagentstryingtocoordinatetheiractions.
CooperativedistributedProblem
NoAgentcansolvetheproblembyitself
Differentcapabilities,resourcesandknowledge
Cooperation:Systemsdointeractto
fulfilltheirtasks
Task&ResultSharing
TaskDecomposition&Allocation
Coordination:Systemsdynamically
adapttheirbehaviortootheragents
MultiagentplanningandTask
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Solutions
Organizations
Taskallocationandmultiagent
planning
Recognizingandresolvingconflicts
Modelingotheragents
Communication
Managingresources
Adaptationandlearning
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CMUCaseStudy
CMUCaseStudy
CMUAgentArchitecture
Abehavior-basedarchitecture.
Flexibleagentroleswithprotocolsforswitching
amongthem.
Collectionofrolesbuiltintoteamformations.
Locker-roomagreement.
Set-plays:Multi-step,multi-agentplansfor
executioninspecificsituations.
http://www.cs.cmu.edu/afs/cs/usr/pstone/public/
papers/98springer/final-champ/final-champ.html
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CMUBehaviors
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CMURoles
Abehaviorisasetofcondition/actionpairs,
whereconditionsarelogicalexpressions
overtheinputsandactionsarebehaviors
Leavesaretheoutputs:internalstate
changesforinternalbehaviorsand
actionprimitivesforexternalbehaviors.
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Specificationofanagent’sinternal
andexternalbehaviours.
Eitherrigid,i.e.completelyspecifyan
agent’sbehaviour,orflexible,i.e.
leaveacertaindegreeofautonomy
totheagentfillingtherole.
Dynamicswitchingofroles.
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CMUFormations
CMURolesandFormations-Example
Decomposethetaskspace.
Consistofasmanyrolesasagents.
Canincludesub-formations,units,
forlocalproblemsolving,
consistingof:
Asubsetoftheformation
Aleader,the
Intra-unitinteractionsamongthe
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CMULocker-RoomAgreement
Aninitialformation.
Aninitialmappingfromagentstoroles.
Orderofprecedencebetweenroles.
Run-timetriggersfordynamicchanging
offormations.
Set-plays.
Syntaxandsemanticsof
communication.
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CMUCommunication
Request/respondballlocation.
Request/respondteammatelocation.
Informpassdestination.
Informgoingtoball.
Informtaking/leavingposition.
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CMUChallenges
ApplyCMUtotheRescueSimulator
Howtorepresentandfollowlocker-room
agreements?
Howtodeterminetheappropriatetimes
foragentstochangerolesand/or
formations?
Howtoensurethatallagentsareusing
thesameformation?
Howtoensurethatallrolesinaformation
arefilled?
Roles
Teamleader
Formation
Strategies
...
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Communication
Communication
“Communicationistheintentional
exchangeofinformationbrought
aboutbytheproductionand
perceptionofsignsdrawnfroma
sharedsystemofconventional
signs.”
RusselandNorvig,1995
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AgentCommunication(1/3)
Communicationinconcurrentsystems:
Synchronizationofmultipleprocesses
CommunicationinObject-OrientedProgramming
Methodinvocationbetweendifferentmodules
CommunicationinMulti-AgentSystems?
Autonomousagentshavecontroloverbothstateand
behavior
Methodsareexecutedaccordingtotheagent’sself-interest
However,agentscanperformcommunicativeactions,i.e.
attempttoinfluenceotheragents
Agentcommunicationimpliesinteraction,i.e.agents
performcommunicationacts
AgentCommunication(2/3)
Exchangeinformationandknowledge.
High-levelcommunication–agent
conversations,suchasnegotiationsand
auctions.
Makeheterogeneousagents
interoperate.
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AgentCommunication(3/3)
Tocommunicateagentsneed:
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SpeechActs(1/2)
MosttreatmentofcommunicationinMASis
inspiredfromspeechacttheory
Thetheoryofspeechactsisgenerally
recognizedtohavebegunwiththeworkofthe
philosopherJohnAustin:“HowtoDoThingswith
Words”(Austin,1962)
Henoticedthatsomeutterancesareratherlike
physicalactionsthatappeartochangethe
stateoftheworld.
acommon
acommonunderstandingof
theknowledgeexchanged;and
theabilitytoexchangethe
aboveinformation.
Awayofdiscoveringotheragents,
networkaddressesandtheir
declaringwar
christening
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SpeechActs(2/2)
TypesofSpeechAct
Atheoryofhowutterancesareusedto
achieveintentionsisaspeechacttheory.
Speechacttheoriesarepragmatictheoriesof
language,i.e.,theoriesoflanguageuse.They
attempttoaccountforhowlanguageisusedby
peopleeverydaytoachievetheirgoalsand
intentions.
Austinidentifiedanumberofperformative
verbs,whichcorrespondtovariousdifferent
typesofspeechacts
Examplesofperformativeverbsarerequest,inform,andpromise
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TypesofSpeechActs
performative=
content=Thebuildingisonfire
speechact=pleasehelpmeextinguishthebuilding
performative=inform
content=Thebuildingisonfire
speechact=Thebuildingisonfire!
performative=
content=Thebuildingisonfire
speechact=Isthebuildingonfire?
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Searle(1969)extendedAustin’sworkandidentified
thefollowingfivekeyclassesofpossibletypesof
speechacts:
Representatives:suchasinforming,e.g.,“Itis
raining”
Directives:attemptstogetthehearertodo
somethinge.g.,“pleasemakethetea”
Commisives:whichcommitthespeakertodoing
something,e.g.,“Ipromiseto…”
Expressives:wherebyaspeakerexpressesa
mentalstate,e.g.,“thankyou!”
Declarations:suchasdeclaringwarorchristening
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PlanBasedSemantics
Howdoesonedefinethesemanticsof
speechacts?Whencanonesay
someonehasuttered,e.g.,arequestor
Cohen&Perrault(1979)definedsemantics
ofspeechactsusingthepreconditiondelete-addlistformalismof(STRIPS)
planningresearch.
Notethataspeakercannot(generally)
forceahearertoacceptsomedesired
mentalstate.
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SemanticsforRequest(A,B,⚔)
SpeechActonlyupdatebelief
pre-conditions:
AbelievesBcando⚔
(youdon’tasksomeonetodosomethingunlessyouthink
theycandoit)
AbelievesBbelievesBcando⚔
(youdon’tasksomeoneunlesstheybelievetheycandoit)
AbelievesAwants⚔
(youdon’tasksomeoneunlessyouwantit)
effect:
BbelievesAbelievesAwantsBtodo⚔
(theeffectistomakethemawareofyourdesire)
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Ontology
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AgentCommunicationLanguages
Inordertobeabletocommunicate,agents
musthaveagreedonacommonsetofterms.
Aformalrepresentationofasetoftermsand
conceptsisknownasanontology.
Realhumanscallthemvocabulary
Theknowledgesharingefforthasassociated
withitalargeeffortatdefiningcommon
ontologies–softwaretoolslikeOntolinguais
developedforthispurpose.
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Anagentcommunicationlanguage(ACL)is
astandardformatforexchanging
messages:
KnowledgeQueryandManipulationLanguage(KQML)
FIPAAgentCommunicationLanguage(FIPAACL)
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KnowledgeSharingEffort
KSE(KnowledgeSharingEffort)inearly
1990sdesignedtwoACLswith
differentpurpose
KQML
TheKnowledgeQueryandManipulation
Language(KQML),whichisan'outer'language
foragentcommunication
TheKnowledgeInterchangeFormat(KIF),a
languageforexpressingcontent,closelybased
onFirstOrderLogic
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KnowledgeInterchangeFormat-KIF(1/2)
KnowledgeInterchangeFormat-KIF(2/2)
Examples:
Aprefixversionoffirstorderpredicate
calculuswithextensionstosupport
non-monotonicreasoningand
definitions.
Itallowsagentsto
“Thetemperatureofm1is83Celsius”:
(=(temperaturem1)(scalar83Celsius))
propertiesofthingsinadomain,e.g.,“Michaelisa
vegetarian”
relationshipsbetweenthingsinadomain,e.g.,“Michael
andJaninearemarried”
generalpropertiesofadomain,e.g.,“Allstudentsare
registeredforatleastonecourse”(quantification∀)
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“Anobjectisabacheloriftheobjectisamanandisnotmarried”:
(defrelationbachelor(?x):=
(and(man?x)(not(married?x))))
“Chip1hasalargersurfacethanchip2”:
(>(*(widthchip1)(lengthchip1))(*(widthchip2)(length
chip2)))
“Anyindividualwiththepropertyofbeingapersonalsohastheproperty
ofbeingamammal”:
(defrelationperson(?x):=>(mammal?x))
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KnowledgeQueryandManipulationLanguage-KQML(1/2)
High-level,message-oriented
communicationlanguageandprotocol
forinformationexchangeindependent
ofcontentsyntaxandapplicable
ontology.
KQMLisdividedintothree
contentlayer
communicationlayer
messagelayer
KnowledgeQueryandManipulationLanguage-KQML(2/2)
Itisan“outer”language,thatdefines
variousacceptable“communicativeverbs”,
orperformatives.Exampleperformatives:
ask-if
(isittruethat…)
perform
(pleaseperformthisaction…)
tell(itistruethat…)
reply(theansweris…)
KnowledgeInterchangeFormatisalanguage
forexpressingmessagecontent.
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KQML-Messagestructure
:contentcontentofthemessage
:languageformallanguageofthemessage
:ontologyterminologyofthemessage
:forcewillsendereverdenycontentof
message?
:reply-withreplyexpected?identifierof
reply?
:in-reply-toidofreply
:sendersenderID
:receiverreceiverID
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KQML-Example(1/3)
(ask-one
:senderjoe
:receiverstock-server
:reply-withibm-stock
:content“(PRICEIBM?price)”
:languageLPROLOG
:ontologyNYSE-TICKS)
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KQML-Example(2/3)
(tell
:senderstock-server
:receiverjoe
:in-reply-toibm-stock
:content“(PRICEIBM14)”
:languageLPROLOG
:ontologyNYSE-TICKS)
KQML-Example(3/3)
(ask-all
:receiverstock-server
:content“price(IBM,[?price,?time])“
:languagestandard_prolog
:ontologyNYSE-TICKS)
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KQMLPerformatives
Basicquery:ask-if,ask-one,ask-all
Multi-response(query):stream-all,eos
Response:error,sorry
Genericinformational:tell,deny,untell,achieve,
unachieve,insert,uninsert
Generator:standby,ready,next,rest,discard
Capability-definition:advertise,unadvertise,
subscribe,recommend-one,recommend-all,brokerone,broker-all
Networking:register,unregister,forward,
broadcast
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KQMLCriticism
ThebasicKQMLperformativesetwas
overlylargeandnotstandardized:
differentimplementationsofKQMLwheredevelopedthat
couldnot,infact,interoperate
Thelanguagewasmissingtheperformative
commissives
Commissivesarecrucialforagentscoordinatingtheir
actions.
Noprecisedefinitionofthetransport
mechanismforKQMLmessages.
Norigoroussemanticsfor
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FIPA
FoundationforIntelligentPhysicalAgents(FIPA)
1997,theFoundationforIntelligent
PhysicalAgents(FIPA)startedworkon
aprogramofagentstandards-the
centrepieceisanACL.
ReleasedspecificationsforFIPAACLin1999and
2002.
BasicstructureisquitesimilartoKQML:
performative;20performativeinFIPA.
housekeeping;e.g.,senderetc.
content,theactualcontentofthemessage.
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FIPAACL
Informperformative
InformandRequestarethetwobasic
performativesinFIPA.Allothersaremacro
definitions,definedintermsofthese.
Inform(j,
Thecontentɸisa
Feasibilitycondition:
Biɸ˄¬Bi(Bifjɸ˅Ui
(ibelievesɸanddoesnotalreadybelievethat
therecipientjisawareofwhetherɸistrueor
Themeaningofinformandrequestis
definedintwoparts:
feasibilitycondition:whichthesendermustsatisfyto
conformtotheFIPAACLstandard.
rationaleffect:whatthesenderofthemessage
attemptstoachieve.
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Rationaleffect:
Bjɸ
(jbelieve
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Requestperformative
Request(j,α)
Thecontentαisanaction.
Feasibility
BiAgent(α,j)˄¬BiIjDone(α)
(ibelievesjwilldoαandthatjdoesnotalready
intendtodoα)
Rationaleffect:
Done(α)
FIPAperformatives
requestinformation:subscribe,query-if,
query-ref
passinginformation:inform,inform-ref,
confirm,disconfirm
negotiation:cfp,propose,accept-proposal,
reject-proposal
performingactions:request,request-when,
request-whenever,agree,cancel,refuse
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FIPAInteractionProtocols
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FIPARequest
InteractionProtocols(IPs)arestandardized
exchangesofperformativesaccordingtowellknown
FIPARequest
FIPAQuery
FIPARequestWhen
FIPAContractNet
FIPAIteratedContractNet
FIPAAuctionEnglish
FIPAAuctionDutch
FIPABrokering
FIPARecruiting
FIPASubscribe
FIPAPropose
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ContractNetProtocol(1/3)
Smith(1980)
Simpleandeasytoimplement
ManagerandSupplierscommunicate
viaoffers
SmithdefinedaContractSpecification
Language
ContractNet
Requirements
Formats
DeadlineforPresentation
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ContractNetProtocol(2/3)
Announcement:Managessendsatask
descriptiontoallpossiblesuppliers
(RequestForBid(T,M))
Bidding:Suppliersevaluatetheofferandsend
aproposaltotheManager(Propose(T,Off,AG)or
NotInterested(T,Ag))
Awarding:ManagerEvaluatestheProposaland
allocatesthecontracttothebestsupplier
(Award(T,Ag,M))
Expediting:Thechosensupplierreplies
positivelyornegativelytotheManager
(Accept(T,Ag),Refuse(T,Ag))
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ContractNetProtocol(3/3)
Rolesarenotspecifiedinadvance,but
aredynamic
TheManagercandecomposeataskand
issueseveralCallforProposals(CFPs)
Alsoacontractormightfurtherdecomposea
taskandgivesomepartsawaytoother
HierarchicalControlStructureforTaskSharing
Typically,anodewilltakeonbothroles,
oftensimultaneouslyfordifferentcontracts
FullyDistributed
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CNPFireBrigadeexample(1/2)
FirebrigadeAneeds
helptoextinguisha
CNPFireBrigadeexample(2/2)
Themanagerawards
acontracttothemost
appropriateagent
Forexample,agent
B,whichiscloserto
thefire
Taskspecification:needed
amountofwater,thelocationof
thefire,andadeadline
AgentBandD
submittheirbits
Thebitcontainsestimatedcosts
fortravelingtothelocationand
forrefillingthetank
Thecontractorsendsbacka
reportafterfinishingthe
taskorfurthersubdivides
thetask...
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LimitationsofContractNets
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FIPAContractNet
Limitations:
Taskdecompositionandproblemsynthesescanbenontrivial
Communicationoverhead
Theawardedcontractormightnotbethebestchoice,a
bettercandidatecouldbetemporarilybusyduringaward
time
Efficiency
Focusedaddressing/directcontracts(e.g.teamstructure)
Agentsendstatusmessage,e.g.eligiblebutbusy,
ineligible,uninterested,…
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CommunicationinRoboRescue
Agentscommunication
Share
Distribute
Coordinate
Lowbandwidthunreliable
JADE
IsitsuitabletouseanACLhere?
Notastandardone:ittakestoomuch
Butsimilarconceptscanbeapplied:inform
andrequestareusefull
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JADE(1/3)
JADE(2/3)
OpenSourceprojectoriginatedby
Telecom(TILAB),currentlygoverned
byaninternationalboard,e.g.
Motorola,FranceTelecom,Whitestein,
JADEallowstherapidcreationof
multi-agentsystemsinJava
Highinteroperabilitythrough
FIPAcompliance
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JADEincludes:
Alibraryfordevelopingagents(which
implementsmessagetransportandparsing)
Aruntimeenvironmentallowingmultiple,parallel
andconcurrentagentactivities
Graphicaltoolsthatsupportmonitoring,logging,
anddebugging
YellowPages,adirectorywhereagentscan
registertheircapabilitiesandsearchforother
agentsandservices
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JADE(3/3)
JADEBehaviors
JADEBehaviors
Abehaviorisbasicallyaneventhandler,amethodwhich
describeshowanagentreactstoanevent:thereceptionofa
messageoratimerinterrupt
TheEventHandlercodeisplacedinamethodcalledaction.
Everybehaviorisscheduledfollowingaroundrobinalgorithm
ExamplesofBehaviorsalreadyincludedinJADE:
SimpleBehavior
CyclicBehavior
TickerBehavior
WakerBehavior
ReceiverBehavior
SequentialBehavior
ParallelBehavior
FSMBehavior
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JADEDebuggingtools
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Summary
ACLsprovidestandardsfor
communicationamongselfishagents,e.g.
withinanopensystems
Motivatedfromthetheoryofspeechacts,
communicationisimplementedinterms
ofactions
TheFIPAACLcanbeconsideredasthe
defactostandardforagent
TheJADEframeworkimplementsitinJAVA
communication
Thereisstilllongwaytogountilwe
havescalablesystems!
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