TheabovecontentisreviewedandannouncedbytheNationalScienceandTechnologyTermReviewCommittee
Въведение в структурата
Сървър-клиент, а именно структура клиент-сървър (C/S). Структурата C/обикновено приема двуслойна структура. Сървърът е отговорен за управлението на данни, а клиентът е отговорен за изпълнението на интерактивните задачи с потребителя.
Theclientisconnectedtotheserverthroughthelocalareanetwork,acceptstheuser'srequest,andmakesarequesttotheserverthroughthenetworktooperatethedatabase.Theserveracceptstheclient'srequest,submitsthedatatotheclient,andtheclientcalculatesthedataandpresentstheresulttotheuser.Theservermustalsoprovidecompletesecurityprotectionanddataintegrityprocessingoperations,andallowmultipleclientstoaccesstheserveratthesametime,whichplaceshighrequirementsontheserver'shardwareprocessingdatacapabilities.
IntheC/Sstructure,theapplicationisdividedintotwoparts:theserverpartandtheclientpart.Theserverpartistheinformationandfunctionssharedbymultipleusers,andperformsback-endservices,suchascontrollingtheoperationoftheshareddatabase;theclientpartisexclusivetotheuser,responsibleforperformingfront-endfunctions,andhaspowerfulfunctionsinerrorprompts,onlinehelp,etc.Function,andcanfreelyswitchbetweensubroutines.
TheC/Sstructureistechnicallymature,anditsmaincharacteristicsarestronginteraction,safeaccessmode,fastresponsespeed,andgoodforprocessinglargeamountsofdata.However,theC/Sstructurelacksversatility.Systemmaintenanceandupgradesneedtoberedesignedanddeveloped,whichincreasesthedifficultyofmaintenanceandmanagement.Furtherdataexpansionismoredifficult.Therefore,theC/Sstructureislimitedtosmalllocalareanetworks.
Опит в разработката
Разработката на модела C/Smodel премина от двустепенна структура към тристепенна структура.
Thetwo-tierstructureconsistsoftwoparts:thefrontendistheclient,whichmainlycompletestheuserinterfacedisplay,acceptsdatainput,verifiesthevalidityofthedata,sendsarequesttothebackgrounddatabase,acceptsthereturnedresult,andprocessestheapplicationlogic;Thebackendistheserver,whichrunstheDBMS,andprovidesdatabasequeryandmanagement.
Thetwo-tierstructurehassomeshortcomings:themainmanifestationsare:poorscalabilityofthesystem;difficultyininteroperatingwithothersystems;difficultyinsupportingmultipleheterogeneousdatabases;frequentinteractionbetweenclientprogramsandserver-sideDBMS,Thenetworktrafficislarge;allclientsneedtoinstallandconfiguredatabaseclientsoftware,whichisaverycomplicatedtask,etc.
Basedontheaboveshortcomingsofthetwo-tierstructure,thethree-tierstructurehasemergedwiththematurityofmiddlewaretechnology.Thecoreconceptistousemiddlewaretodividetheapplicationintothreedifferentprocessinglevels:thepresentationlayer,thebusinesslogiclayer,andthedatastoragelayer.
Thethree-tierstructurehascertainadvantagesoverthetwo-tierstructure:ithasgoodopenness;itreducesthecostoftheentiresystemandisveryconvenienttomaintainandupgrade;thesystemhasgoodscalability;thesystemmanagementissimpleandcansupportHeterogeneousdatabaseshavehighavailability;strictsecuritymanagementcanbecarriedout.
AdvantagesandDisadvantages
Advantages
TheadvantageoftheC/SstructureisthatitcangivefullplaytotheprocessingcapabilitiesoftheclientPC,andmanytaskscanbeprocessedbytheclient.Submittotheserver.Thecorrespondingadvantageisthattheclientrespondsquickly.Thespecificmanifestationsareinthefollowingtwopoints:
(1)Theapplicationserverhasalighterdataload.ThesimplestdatabaseapplicationofC/Sarchitectureconsistsoftwoparts,namelyclientapplicationanddatabaseserverprogram.Thetwocanbecalledtheforegroundprogramandthebackgroundprogram,respectively.Themachinerunningthedatabaseserverprogramisalsocalledtheapplicationserver.Oncetheserverprogramisstarted,itisalwayswaitingtorespondtotherequestsentbytheclientprogram;theclientapplicationprogramrunsontheuser'sowncomputer,correspondingtothedatabaseserver,whichcanbecalledtheclientcomputer,whenanyoperationonthedatainthedatabaseisrequired,Theclientprogramautomaticallyfindstheserverprogramandsendsarequesttoit.Theserverprogramrespondsaccordingtopredeterminedrulesandsendsbacktheresult.Theapplicationserverrunsalighterdataload.
(2)Thedatastoragemanagementfunctionisrelativelytransparent.Indatabaseapplications,thedatastoragemanagementfunctionisperformedindependentlybytheserverprogramandtheclientapplicationprogram,andusuallythosedifferent(whetherknownorunknown)front-endapplicationscannotviolatetherulesintheserverprogramCentralizedimplementation,suchasthevisitor'sauthority,thenumbercanberepeated,theremustbeacustomertoestablishsuchrulesasorders.Alloftheseare"transparent"totheenduserswhoworkontheforegroundprogram,andtheycancompletealltheirworkwithouthavingtointervene(andusuallycannotinterfere)withtheprocessbehindit.Intheapplicationoftheclient-serverarchitecture,theforegroundprogramisnotvery"skinny",andallthetroublesomethingsarehandedovertotheserverandthenetwork.UndertheC/Ssystem,thedatabasecannottrulybecomeapublicandspecializedwarehouse,anditissubjecttoindependentandspecializedmanagement.
Disadvantages
WiththerapiddevelopmentoftheInternet,mobileofficeanddistributedofficearebecomingmoreandmorepopular,whichrequiresoursystemtobeexpandable.Thiswayofremoteaccessrequiresspecializedtechnology,andthesystemmustbespeciallydesignedtohandledistributeddata.
Theclientneedstoinstallspecialclientsoftware.Firstly,itinvolvestheworkloadofinstallation,andsecondly,anycomputerproblems,suchasvirusesorhardwaredamage,needtobeinstalledormaintained.Especiallyinthecaseofmanybranchesorspecialtystores,itisnotaproblemofworkload,butaproblemofdistance.Inaddition,whenthesystemsoftwareisupgraded,eachclientneedstobereinstalled,anditsmaintenanceandupgradecostsareveryhigh.
По принцип има ограничения за операционната система на клиента. Може да се адаптира към Win98, но не може да се използва в Windows 2000 или Windows XP. Или да не се прилага към новата операционна система на Microsoft и т.н., да не говорим за Linux, Unix и т.н.[1](В момента повечето клиенти са адаптирани към системата winXP, но не могат да се използват за новата операционна система на Microsoft или други системи за разработка.)
AlthoughthetraditionalC/SarchitectureisOpenmode,butthisisonlythefirst-levelopennessofsystemdevelopment.Inaspecificapplication,boththeClientsideandtheServersideneedspecificsoftwaresupport.Sinceitfailstoprovidetheopenenvironmentthatusersreallyexpect,thesoftwareoftheC/Sstructureneedstodevelopdifferentversionsofsoftwarefordifferentoperatingsystems,andtheproductupgradesareveryfast,itisdifficulttoadapttothesimultaneoususeofLANuserswithmorethan100computers.Moreover,thecostishighandtheefficiencyislow.
ThedisadvantagesoftheC/Sarchitectureincludehighmaintenancecostsandlargeinvestments.Firstofall,usingtheC/Sarchitecture,itisnecessarytoselectanappropriatedatabaseplatformtorealizethetrue"unification"ofdatabasedata,sothatthesynchronizationofthedatadistributedinthetwoplacesiscompletelymanagedbythedatabasesystem,butlogicallytheoperatorsinthetwoplacesmustdirectlyAccesstothesamedatabasecanbeeffectivelyachieved.Therearesomeproblems.Ifyouneedtoestablish"real-time"datasynchronization,youmustestablishareal-timecommunicationconnectionbetweenthetwoplacesandkeepthedatabaseserversrunningonline.ThenetworkmanagementstaffmustMaintenanceandmanagementoftheserverandthemaintenanceandmanagementoftheclientarerequired,whichrequireshighinvestmentandcomplextechnicalsupport,highmaintenancecosts,andalargeamountofmaintenancetasks.
Secondly,thetraditionalC/Sstructuresoftwareneedstodevelopdifferentversionsofsoftwarefordifferentoperatingsystems.Becausetheproductisupdatedveryquickly,thecostandlowefficiencyarenolongersuitableforworkneeds.Aftertheemergenceofcross-platformlanguagessuchasJAVA,theB/SarchitectureviolentlyimpactsC/Sandposesthreatsandchallengestoit.
Характеристики на сървъра:
1.Пасивна роля (роб).
2. Изчакване на заявка от клиента.
3. Обработете заявката и върнете резултата.
Характеристики на клиента:
1.Активна роля (главна).
2.Изпратете заявка.
3. Изчакайте, докато не получите отговор.
C/SandB/S
Сравнение на хардуерна среда
CSisbuiltonthebasisoflocalareanetworks,betweenlocalareanetworksThenprovideconnectionanddataexchangeservicesthroughadedicatedserver.IntheCSstructure,boththeclientandtheserverneedtoprocessdatatasks,whichplaceshigherrequirementsontheclient'shardware.TheBSstructureisbuiltonthewideareanetworkanddoesnotneedtobeequippedwithadedicatednetworkhardwareenvironment.Althoughthehardwarerequirementsfortheclientsidearenotveryhigh,onlytheoperatingsystemandbrowserarerequiredtorun,buttheserversideneedstoprocessalargeamountofreal-timedata,whichplaceshigherrequirementsontheserversidehardware.Generallyspeaking,theBSstructurecangreatlyreducethecostcomparedwiththeCSstructure.
Сравнение на системната поддръжка и надграждане
EveryclientintheCSstructuremustinstallandconfigurerelatedsoftware,suchasoperatingsystemandclientsoftwareWait.Whentheclientsoftwareneedstobemaintainedandupgraded,evenifonlyacertainfunctionisaddedordeleted,alltheclientsoftwareintheCSstructureneedstobeuninstalledandreinstalledonebyone.Ifyoudonotupgrade,youmayencounterthesituationwheretheclientsoftwareversionisinconsistentandcannotwork.EachclientintheBSstructurecanprocessvariousinformationonlythroughthebrowser,withouttheneedtoinstallclientsoftware.Almostalltaskssuchasmaintenanceandupgradesareperformedontheserverside.Ifthesystemneedstobeupgraded,onlyJustinstalltheupgradeprogramontheserverside.
Сравнение на сигурността на системата
TheCSstructureadoptsapoint-to-pointstructuremode,andthedataprocessingisbasedonanetworkprotocolwithhighersecurity.Inaddition,CSisgenerallyorientedtoarelativelyfixedusergroup.Itcanperformmulti-levelverificationofpermissions,andhasastrongabilitytocontrolinformationsecurity,andsecuritycanbewellguaranteed.TheBSstructureadoptsanopenstructuremodelofpoint-to-multipointandmulti-point-to-multipoint.Itssecuritycanonlybeguaranteedbythedatabasethatmanagesthepasswordonthedataserver.Moreover,thenetworksecuritytechnologyisnotyetmature,anditneedstobecontinuouslydiscoveredandrepaired.Securitybreach.
Интерфейс на фюзера за сравнение
TheCSstructureismostlybuiltontheWindowsplatform,withlimitedperformancemethods,andgenerallyhigherrequirementsforprogrammers.TheBSstructureisbuiltonthebrowser,whichhasaricherandmorevividwayofcommunicatingwithusers.
Обработка на сравнение
TheCSstructureisbuiltonalocalareanetwork,andtheprocessingisorientedtoarelativelyfixedusergroupinthesamearea,andmeetstherequirementsforhighsecurity.Requirementsarerelatedtotheoperatingsystem.TheBSstructureisbuiltontheWAN,dealingwithdifferentusergroupsinscatteredareas,andhaslittlerelationtotheoperatingsystem.Inaddition,comparedwiththeCSprocessingmode,theBSprocessingmodesimplifiestheclientsideandonlyneedstoinstalltheoperatingsystemandbrowser.
Сравнение на повторно използване на софтуер
CSstructuresoftwarecanbeconsideredfromtheinevitableintegrity,andthereusabilityofcomponentsisnotasgoodasthereusabilitybuiltundertherequirementsofBSgood.BScorrespondstomultiplestructures,requiringrelativelyindependentfunctionstobeconstructed,whichcanbereusedrelativelywell.
Сравнение на скоростта на системата
TheCSstructureisonelesslogicalstructurethantheBSstructure.Forthesametask,theCSstructurecompletesfasterthanThefaststructureofBSmakesCSmoreconducivetoprocessinglargeamountsofdata.Inaddition,sincetheclientisdirectlyconnectedtotheserver,thereisnointermediatelink,sotheresponsespeedisfast.
Сравнение на интерактивност и поток от информация
TheinteractivityoftheCSstructureisverystrong.IntheCSstructure,theclienthasacompleteclientsoftware.Itcanhandlealargenumberofreal-timedatastreams,andtheresponsespeedisfast.AlthoughtheBSstructurecanprovidecertaininteractivecapabilities,theinteractivecapabilitiesareverylimited.TheinformationflowofCSissingle,whilethestructureofBScanprocessinformationsuchasB-B,B-C,B-G,etc.,withchangesinflowdirection.