文献翻译基于代理的分布式应用发展的技术文档格式.docx

文献翻译基于代理的分布式应用发展的技术文档格式.docx

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Technologiesforthe

DevelopmentofAgent-basedDistributedApplications

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2008.3.12

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TechnologiesfortheDevelopmentofAgent-basedDistributedApplications

　　Mobileagentcomputingisanextensionoftheearlierideaof"

processmigration."

Mobileagenttechnologyoffersseveralpotentialbenefitsoverconventionalclient-servercomputingthatcouldhelpimproveclassicdistributedsystemsdesigns,whichareusuallybasedonthewell-knownremoteprocedurecall（RPC）oritsobject-orientedequivalent,remotemethodinvocation（RMI）.

　　Mobilesoftwareagentsenableashiftinthecommunicationsparadigmofdistributedsystemsfromwhatiscalled"

datashipping"

to"

functionshipping."

KeytothisshiftisthehigherlevelofabstractionthatamobilesoftwareagentcanprovidecomparedtoaRPCoraRMIcallbecauseitscodeisautonomous.Thisautonomyshouldtheoreticallyreducenetworkloadandcommunicationoverheadindistributedapplicationsaswellasfacilitatethedevelopmentofapplicationsforpotentiallyunreliable,networkedcomputingenvironments.

　　Furthermore,andperhapsevenmoreimportantly,awidespreadagent-enabledinfrastructureprovidesacommonplatformfordistributedapplicationsofarbitrarypurpose.ConsiderthePostScriptexamplegivenbyChess,Harrison,andKershenbaumtoillustratetheadvantagesastandardizedmobileagentexecutionenvironmentoffers.PostScriptdocumentsareprogramsexecutedbyaPostScriptinterpreterandsenttoprintserversthatonlyacceptpassiveinputtext,e.g.,MicrosoftWordfiles.Thedrawbackofthelattermethodisobvious:

foreverynewdocumentformat,allprintserversintheworldwouldhavetobeupdated.Theexampleiseasilytransferredtomobileagentcomputing:

mobileagentsasageneral-purposecomputingplatformdonotrequireanyspecificfunctionstobeimplementedintheservers,suchasfull-textretrievalmethodsordatabaseinterfaces.

　　DistributedapplicationsbasedonRPC-liketechniquesmightnotbeeasytoadapttolarge-scale,heterogeneous,andpotentiallyunreliableenvironments,liketheInternet,becauseimplementationofRPC-stylesemanticsreliesonrelativelystaticandreliablesystemstructures.Combiningmobileagenttechnologywithwell-establishedmechanismsmightpotentiallyleadtosystemsmuchbettersuitedtotheneedsofInternet-likecomputingenvironments.

　　Tobeabletoclearlydistinguishwhatinthiscontextisreferredtoas"

conventional"

client-servertechnologyfrommobileagenttechnology,sometermsneedfirstbedefined.

　　Agent

　　AsdefinedbytheObjectManagementGroup（OMG）,anorganizationthatdevelopsstandardsforcomponent-basedsoftwaresystems,anagent"

isacomputerprogramthatactsautonomouslyonbehalfofapersonororganization."

　　MobileAgent

　　Amobileagentisanobjectthatis"

notboundtothesystemwhereitbeginsexecution.Ithastheuniqueabilitytotransportitselffromonesystemwithinanetworktoanother."

　　Place

　　Aplaceis"

acontextwhereanagentcanexecute."

.Furthermore,thetermsagentplatformandagentsystemwillbeusedsynonymouslyaccordingtotheOMGdefinition:

　　"

Anagentsystemisaplatformthatcancreate,interpret,execute,transfer,andterminateagents.Likeanagent,anagentsystemisassociatedwithanauthoritythatidentifiesthepersonororganizationforwhomtheagentsystemacts."

　　Becausemobileagenttechnologyisageneral-purposecomputingplatform,ithasbeencalleda"

solutioninsearchofaproblem."

Inthefollowing,wewillexaminetheadvantagesthatsuchaplatformoffersfordistributedandparallelcomputingandtheproblemsthatpreventitswidespreadsuccess.Subsequently,abriefoverviewofstate-of-the-artagentsystemsisprovided,togetherwithanexaminationofhowthesesystemsaddressthecontinuingchallengesofmobileagentcomputing.

　　Mobileagentsasadesignparadigmfordistributedsystems

　　Theconceptoftransmittingexecutableprogramsbetweenpotentiallyheterogeneousexecutionenvironmentsintroducesanewparadigmfortheimplementationofdistributedapplicationsforlarge-scale,potentiallyunreliable,networkedenvironments.Intraditionalclient-serversystemsthatuseonlyRPC,thedatatobemanipulated,suchastext,relationaldata,andimages,ismovedbetweenproceduresalreadyresidingontheclientandtheserver.Agent-basedcomputing,however,facilitatesthetransportationoftheprocedureitself（thatis,thealgorithmtobeapplied）totheclientbymeansofamobileagent,whichcanleadtolesstraffic.

　　Alsointeresting,isthepossibilityofimplementingdynamicapplicationprogramminginterfaces（API）overagentsthroughtheuseofanagentcommunicationlanguage;

suchalanguag