Server-klient

TheabovecontentisreviewedandannouncedbytheNationalScienceandTechnologyTermReviewCommittee

Úvod do struktury

Server-klient, jmenovitě struktura Klient-Server(C/S). Struktura C/Struktura obvykle přijímá dvouvrstvou strukturu. Server je odpovědný za správu dat a klient je odpovědný za dokončení interaktivních úloh s uživatelem.

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.

Zkušenosti s vývojem

Vývoj modelu C/S přešel z dvouvrstvé struktury na třívrstvou.

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.

Obecně platí omezení na klientský operační systém. Může být přizpůsoben pro Win98, ale nelze jej použít ve Windows 2000 nebo Windows XP. Nebo jej nelze použít pro nový operační systém Microsoft atd., natož Linux, Unix atd.[1](Momentálně nelze načíst pro většinu nových klientů P pro softwary. systém nebo jiné vývojové systémy.)

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-platformlanguages​​suchasJAVA,theB/SarchitectureviolentlyimpactsC/Sandposesthreatsandchallengestoit.

Charakteristika serveru:

1.Passiverol (otrok).

2. Čekání na požadavek od klienta.

3. Zpracujte požadavek a vraťte výsledek.

Charakteristika klienta:

1.Activerol(hlavní).

2. Odeslat žádost.

3.Počkejte, až obdržíte odpověď.

C/SandB/S

Porovnání hardwarového prostředí

CSisbuiltonthebasisoflocalareanetworks,betweenlocalareanetworksThenprovideconnectionanddataexchangeservicesthroughadedicatedserver.IntheCSstructure,boththeclientandtheserverneedtoprocessdatatasks,whichplaceshigherrequirementsontheclient'shardware.TheBSstructureisbuiltonthewideareanetworkanddoesnotneedtobeequippedwithadedicatednetworkhardwareenvironment.Althoughthehardwarerequirementsfortheclientsidearenotveryhigh,onlytheoperatingsystemandbrowserarerequiredtorun,buttheserversideneedstoprocessalargeamountofreal-timedata,whichplaceshigherrequirementsontheserversidehardware.Generallyspeaking,theBSstructurecangreatlyreducethecostcomparedwiththeCSstructure.

Porovnání údržby a upgradu systému

EveryclientintheCSstructuremustinstallandconfigurerelatedsoftware,suchasoperatingsystemandclientsoftwareWait.Whentheclientsoftwareneedstobemaintainedandupgraded,evenifonlyacertainfunctionisaddedordeleted,alltheclientsoftwareintheCSstructureneedstobeuninstalledandreinstalledonebyone.Ifyoudonotupgrade,youmayencounterthesituationwheretheclientsoftwareversionisinconsistentandcannotwork.EachclientintheBSstructurecanprocessvariousinformationonlythroughthebrowser,withouttheneedtoinstallclientsoftware.Almostalltaskssuchasmaintenanceandupgradesareperformedontheserverside.Ifthesystemneedstobeupgraded,onlyJustinstalltheupgradeprogramontheserverside.

Porovnání zabezpečení systému

TheCSstructureadoptsapoint-to-pointstructuremode,andthedataprocessingisbasedonanetworkprotocolwithhighersecurity.Inaddition,CSisgenerallyorientedtoarelativelyfixedusergroup.Itcanperformmulti-levelverificationofpermissions,andhasastrongabilitytocontrolinformationsecurity,andsecuritycanbewellguaranteed.TheBSstructureadoptsanopenstructuremodelofpoint-to-multipointandmulti-point-to-multipoint.Itssecuritycanonlybeguaranteedbythedatabasethatmanagesthepasswordonthedataserver.Moreover,thenetworksecuritytechnologyisnotyetmature,anditneedstobecontinuouslydiscoveredandrepaired.Securitybreach.

Porovnání rozhraní fixačního zařízení

TheCSstructureismostlybuiltontheWindowsplatform,withlimitedperformancemethods,andgenerallyhigherrequirementsforprogrammers.TheBSstructureisbuiltonthebrowser,whichhasaricherandmorevividwayofcommunicatingwithusers.

Porovnání při zpracování

TheCSstructureisbuiltonalocalareanetwork,andtheprocessingisorientedtoarelativelyfixedusergroupinthesamearea,andmeetstherequirementsforhighsecurity.Requirementsarerelatedtotheoperatingsystem.TheBSstructureisbuiltontheWAN,dealingwithdifferentusergroupsinscatteredareas,andhaslittlerelationtotheoperatingsystem.Inaddition,comparedwiththeCSprocessingmode,theBSprocessingmodesimplifiestheclientsideandonlyneedstoinstalltheoperatingsystemandbrowser.

Porovnání opětovného použití softwaru

CSstructuresoftwarecanbeconsideredfromtheinevitableintegrity,andthereusabilityofcomponentsisnotasgoodasthereusabilitybuiltundertherequirementsofBSgood.BScorrespondstomultiplestructures,requiringrelativelyindependentfunctionstobeconstructed,whichcanbereusedrelativelywell.

Porovnání rychlosti systému

TheCSstructureisonelesslogicalstructurethantheBSstructure.Forthesametask,theCSstructurecompletesfasterthanThefaststructureofBSmakesCSmoreconducivetoprocessinglargeamountsofdata.Inaddition,sincetheclientisdirectlyconnectedtotheserver,thereisnointermediatelink,sotheresponsespeedisfast.

Porovnání interaktivity a toku informací

TheinteractivityoftheCSstructureisverystrong.IntheCSstructure,theclienthasacompleteclientsoftware.Itcanhandlealargenumberofreal-timedatastreams,andtheresponsespeedisfast.AlthoughtheBSstructurecanprovidecertaininteractivecapabilities,theinteractivecapabilitiesareverylimited.TheinformationflowofCSissingle,whilethestructureofBScanprocessinformationsuchasB-B,B-C,B-G,etc.,withchangesinflowdirection.