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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文献、资料发表(出版)日期:
2008.3.12
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外文文献:
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