Genetic algorithms using multi-objectives(11)

WewillusethenotionofzonefortheroundupofentitiesontheGanttdiagram,whilewewillspeakaboutthenotionofgroupfortheroundupofentitiesofsimilarorclosenature.Sinceagentshavetoin-terveneongroupsandelementaryentities,theMASwillthenbecomposedofmicro-andmeta-agents.Itisthereforeimportantforthisevolution,tointroduceagentshavinganevolvingcharacter:themeta-agentsofevolution.Thesemeta-agents’functionwillbetomakethisorganizationevolvebymeansofa

geneticalgorithmestablishingasexualreproductionofagents.Itisinterestingtonotethat,traditionally,agentsonlyclonethemselves.Buthere,weuseage-neticalgorithmforthephysicalevolutionoftheagents[28,29].Inthecourseoftheevolution,differentagentgranularitiesappear.Wehavethereforemicroandmeta-agentsthataregoingtointervene,accordingtotheirgranularity,onanentityoragroup,bypassingthroughintermediatelevels.Thus,agentshavingameta-knowledgearegoingtobeabletointerveneonthemacro-entities(groups)aswellasonsomezonesoftheGanttdiagram.Thus,thereisadistributedagentsystembeingabletomutateandhostingagentsabletoachieveacrossoverbasedreproductionbetweenthem.

8.Acontractnetbasedapproach

Thecontractnetisaprotocolfortheresolutionofdistributedproblem,de nedbySmith[48].Themainobjectiveofthisprotocolbeingthenegotiation,itpro-ceedsbyallocationoftaskstoasetofproblemsolversandusestheconceptofnegotiationtograntcontracts.Thebasicarchitecturecontainsnodeshavingachiefandcarryingroles[7].8.1.Thecontract-netprocotol

Contract-netbasedsystemsrepresentaconceptthatcanbeusedtoestablishmechanismsofcooper-ationbetweenagents[6].Acontractnetconsistsofanumberofnodesthatarerepresentedbyindivid-ualagents.Byanalogytoasalesession,suspendedsub-tasksareopenlyproposedtoauctionstowhicheachnodecanreplyaccordingtotheinterestthatithasforthissub-task.Thestageoftaskattributionrep-resentsaprocessinwhichallthenodes(agents)areassociated.Theideaistousetheavailableresourcesandtheexistingknowledgeofagentsasef cientlyaspossible[51];thatistosaybyallocationofonesub-tasktotheagentwhichisthemostapttooperateatagivenmoment.Thecontract-netprotocolformstheskeletonofoursystem.Itisde nedbyalan-guagebetweenthenodesthatcanbeunderstoodbythesetofagents.Thecommunicationbetweenagentsisalwaysbasedonthenotionofan“acceptancemessage”.Thisspeci cityde nestheexactroleofanagent.