robust-systems

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1、BuildingRobustSystemsanessayGeraldJaySussmanMassachusettsInstituteofTechnologyJanuary13,2007AbstractItishardtobuildrobustsystems:systemsthathaveaccept-ablebehavioroveralargerclassofsituationsthanwasanticipatedbytheirdesigners.Themostrobustsystemsareevolvable:theycanbeeasilyadaptedtone

2、wsituationswithonlyminormod-ication.Howcanwedesignsystemsthatare exibleinthisway?Observationsofbiologicalsystemstellusagreatdealabouthowtomakerobustandevolvablesystems.Techniquesorigi-nallydevelopedinsupportofsymbolicArticialIntelligencecanbeviewedaswaysofenhancingrobustnessandevolv

3、abilityinprogramsandotherengineeredsystems.Bycontrast,commonpracticeofcomputerscienceactivelydiscouragestheconstruc-tionofrobustsystems.1RobustnessItisdiculttodesignamechanismofgeneralutilitythatdoesanypartic-ularjobverywell,somostengineeredsystemsaredesignedtoperformaspecicjob.Gene

4、ral-purposeinventions,suchasthescrewfastener,whentheyappear,areofgreatsignicance.Thedigitalcomputerisabreak-throughofthiskind,becauseitisauniversalmachinethatcansimulateanyotherinformation-processingmachine.Wewritesoftwarethatconguresourcomputerstoeectthissimulationforthespecicjob

5、sthatweneeddone.Wehavebeendesigningoursoftwaretodoparticularjobsverywell,asanextensionofourpastengineeringpractice.Eachpieceofsoftwareisdesignedtodoarelativelynarrowjob.Astheproblemtobesolvedchanges,thesoftwaremustbechanged.Butsmallchangestotheproblemtobesolveddonotentailonlysmallchan

6、gestothesoftware.Softwareisdesignedtootightlyfortheretobemuch exibility.Asaconsequence,systemsdonotevolvegracefully.Theyarebrittleandmustbereplacedwithentirelynewdesignsastheproblemdomainevolves.1Thisisslowandexpensive.Ourengineeredsystemsdonothavetobebrittle.TheInternethasadaptedfrom

7、asmallsystemtooneofglobalscale.Ourcitiesevolveor-ganically,toaccommodatenewbusinessmodels,lifestyles,andmeansoftransportationandcommunication.Indeed,fromobservationofbiologicalsystemsweseethatitispossibletobuildsystemsthatcanadapttochangesintheenvironment,bothindividuallyandasanevolut

8、ionar