The RoleX Environment for Multi-Agent Cooperation

TheRoleXEnvironmentforMulti-AgentCooperationGiacomoCabri,LucaFerrari,LetiziaLeonardiDipartimentodiIngegneriadell’InformazioneUniversitàdiModenaeReggioEmiliaViaVignolese,905–41100Modena–ITALY{cabri.giacomo,ferrari.luca,leonardi.letizia}@unimo.itAbstract.InthispaperwepresenttheRoleXenvironmentformulti-agentsystems.Borntosupportthemanagementofrole-basedinteractions,Rolexprovidesdifferentservices,inparticulartosupportopenandflexiblecooperation.Tothispurpose,RoleXexploitsanevent-basedcommunicationmechanismandadoptsSOAPasmessageencoding.SuchfeaturesmakeRoleXwellsuitdynamicandunpredictablescenariossuchastheInternet.1IntroductionCooperationinmulti-agentapplicationrequiresanappropriatesupportfortheinteractionoccurringbetweenagents.BRAIN[10]isarole-basedframeworkforsupportingthedevelopmentofinteractionsinmulti-agentapplications.Wehavebasedthisframeworkonrolestoexploittherelatedadvantages.First,rolesenableaseparationofconcernsbetweenthedifferentissuesindevelopingagent-basedapplications[8].Second,theypermitthereuseofsolutionsandexperiences;infact,rolesarerelatedtoanapplicationscenario,anddesignerscanexploitrolespreviouslydefinedforsimilarapplications.Therefore,rolescanalsobeseenasasortofdesignpatterns[20]:asetofrelatedrolesalongwiththedefinitionofthewaytheyinteractcanbeconsideredasawell-definedcooperationpatternthatcanbereusedindifferentbutsimilarsituations.InsideBRAIN,wehavedevelopedanenvironment,calledRoleX,whichsupportsthedynamicassumptionofrolesbyagents[4],throughtheruntimemanipulationoftheagentcode.Inaddition,RoleXprovidesservicesrelatedtoopennessandinteroperability,andaimsatmakingagentsinteractinaflexibleandinteroperableway.Tothispurpose,weexploittheevent-basedcommunication,whichwellsuitsdynamicandunpredictablesituationsandmakestheRoleXenvironmentanactiveentityininteractions.Moreover,theadoptionoftheSOAPprotocolenablesagentstointeractwithavarietyofotherkindsofentitiesandinparticularinformationsources.InthispaperwereportonthedesignandtheimplementationoftheRoleXenvironment,explainingtheservicesthatitmakesavailable.RoleXtakesintoaccountalsomobileagents,whichgrantfurtherflexibilityandincreasethedynamismofapplications.Interestedreaderscanfindmoreinformationabouttheadoptedmodelin[10].Thispaperisorganizedasfollows.Section2sketchesanoverviewoftheBRAINframework.Section3explainsthedesignoftheRoleXenvironment,reportingourchoices;anapplicationexampleinthefieldofe-democracyisexploitedtomaketheconceptsconcrete.Section4showssomedetailsabouttheimplementationofRoleX.Section5reportssomerelatedworkand,finally,Section6concludesthepaper.2OverviewoftheBRAINFrameworkTheBRAINframework[10]aimsatsupportingthedevelopmentofinteractionsinmulti-agentapplicationsandiscomposedof(i)awell-definedmodelforroles,(ii)XRole,anXML-basednotationforagentroles,and(iii)possiblyseveralenvironmentswhichimplementthepreviousmodelandexploittheXRolenotation.Arolecanbeconsideredasastereotypeofbehaviorcommontodifferentagentsinagivensituation.Suchabehaviorisexhibitedbyagents,butisalsoexpectedbyotherentities,mainlyotheragents,organizations[31]andenvironments.Itisusefultodealwithrolesseparatelyfromtheagents.Inourapproacharoleismodeledasasetofcapabilitiesandanexpectedbehavior,bothappliedtotheagentthatplayssuchrole.Thismodelofroleleadstoatwofoldviewpointoftherole:fromtheapplicationpointofview,theroleallowsasetofcapabilities,whichcanbeexploitedbyagentstocarryouttheirtasks;fromtheenvironmentpointofview,theroleimposesadefinedbehaviortotheentitiesthatassumesit.Theformerpointisthataroleisasetofcapabilitiesthatagentsplayingagivenrolecanperform.Thistakesintoaccounttheproactivenessfeatureofagents,sincetheyhavetoperformactionstocarryouttheirtasks,andso,theymustbeenabledtodoit.Thelatterpointisthatanagentplayingagivenroleisexpectedtoexhibitaspecificbehavior.Thisaccountsfortheagent’sreactivity,sincetheyaresensibletowhathappensintheenvironmentwheretheylive.The“expectedbehavior”isconstitutedbythereactionstoexternalstimuli.ThenotationproposedbyBRAIN,calledXRole[7],enablesthedefinitionofrolesbymeansofXMLdocuments;thisgrantsinteroperabilityandallowsdifferentrepresentationstailoredontheneedsofthedifferentphasesoftheapplicationdevelopment.Itisworthnotingthateachdifferentrepresentationderivesfromthesameinformation,sothedifferentphasesofthedevelopmentofapplicationsrelyonthesameinformation,grantingcontinuityduringtheentiredevelopment.Forinstance,duringtheanalysisphase,theanalystscreateXRoledocumentsfollowingtheappropriateXMLSchema,whichguidestheminthedefinitionoftherolefeatures.TheseXRoledocumentscanbetranslatedintoHTMLdocumentstoprovidehigh-leveldescriptionsalsoforfurtheruses.Inthedesignphase,thesameXRoledocumentscanbetranslatedintomoredetailedHTMLdocumentstosuggestfunctionalitiesoftheinvolvedentities.Finally,attheimplementationphase,againthesameXRoledocumentscanbeexploitedtoobtainJavaclassesthatimplementtheroleproperties.3DesignoftheRoleXEnvironmentRoleXisoneofthepossibleenvironmentsimplementedtosupporttheBRAINframework.So,itadoptstheBRAINrolemodelandexploitstheXRolenotation.InRoleX,capab