可編程控制器的數(shù)據(jù)庫系統(tǒng)畢業(yè)論文外文翻譯

DatabaseSystemsforProgrammableLogicControllersABSTRACTInthispaper,weidentifythedatabaseissuesassociatedwithprogrammablelogiccontrollers(PLC),special-purposecomputersusedinscientificandindustrialapplications,e.g.infactoriesinmanufacturingenvironments.WeproposeasaPLCdatabasesystemasingle-user,real-time,scalablemain-memory-onlyrelationaldatabasesystemwithatwo-levelarchitecturehavinghistoricaldatamodelingandmanipulationcapabilities,andqueryprocessingtechniquesincorporatingtime-and/orerror-constrainedqueryevaluation.Werevisetheladderlogiclanguage,themostcommonPLClanguage,toincorporatedatamanipulationlanguageinstructions.WeaddaseparatetimecomponentintothePLCprocessorscantimetohandledatabaseupdates,backup,integrityenforcementanddataarchivalissues.1.IntroductionAprogrammablelogiccontroller(PLC)isaspecial-purposecomputerusedwithinreal-timescientificcomputingsystems,andindustrialcontrolsystems,say,theautomatedcontrolofafactory'smachinery-therunningexampleusedinthispaper.ThispaperisapositionpaperthatproposesaPLCdatabasesystemanddiscussesitsfeatures.Indoingso,wetouchbaseswithanumberofbasicdatabasetopics,and,thus,frequentlyrefertootherworkfordetails.PLCsaremostlyusedinmanufacturingenvironments-hence,thechoiceofourrunningexample.However,PLCsarealsousedinscientificapplicationsforsignaldatagatheringandpreliminarydataprocessing.Thus,wethinkthatforsomescientificapplications,aPLCdatabasemayalsoserveasalocal/transientpartofalargerscientificdatabase.Withtherapidadvancesincomputerhardwareandfallingmemoryprices,inrecentyears,thecapabilitiesofthenewPLCsinthemarketplacehavebeenincreasingdramatically.ThispaperisapositionpaperthatarguesthataPLCsoftwarecannowcontainadatabasesystemtogreatlyincreaseitsfunctionality.WeproposethearchitectureinFigure1asthearchitectureofanenvironmentwherereal-timedatagathering(frommultiplesensors)andreal-timedatamanipulationtakesplace.WenowlisttheadvantagesofhavingadatabasesystemdirectlyinsideaPLC.(1)DataModelingTechniques:Theinputandoutputbuffersrepresentaratherunorganizedtransientmodeloftherealworld,andhence,carlbemodeledbetterusingthetraditionaldatamodelingtechniquesofdatabases.(2)HistoricalDatabases:PLCsroutinelydealwithdifferentversionsofdataovertime.Therefore,historicaldatamodelingtechniquesaswellashistoricaldatamanipulationtechniquescanreplacetheadhocwaysofmanipulatinghistoricaldatainPLCs.(3)User-FriendlyInterfaces:Presentlyinthemarketplace,thePLCsoftwareandindustrialterminalsallowalimiteddisplayofmessagesandvariable-datainformationinmemory.Forexample,thecontacthistogramfunctiondisplaystheon/offhistoryofaspecificmainmemory.(4)HandlingLargeVolumesofData:Withtheaddedcapabilitiesofadatabaseandaquerylanguage,thePLCmayanalyzemuchlargervolumesofdata.(5)DataReductionandCompactionatthePLCLevel:Presently,forfurtheranalysisorsimplyduetovariousregulations,datacollectedbyPLCsgettransmittedandstoredintoahostcomputeranarchitectureshown..SincethepresentPLCscannotsatisfactorilyanalyzemostdata,theysimplytransmitdatatothehostcomputer.Insomescientificexperimentsandapplications,thedatagatheredissolargethatargumentshavebeenraisedfor"processingthedataon-the-fly"duringtheexecutionofanexperiment/transaction[SSDB86](a)Real-TimeDatabase:Thedataintheinputbuffermustbescannedwithinreasonablyshort"real-time"intervalsrangingfrommicrosecondstoseconds.Therefore,responsestoqueriesmustbeguaranteedtobelessthanacertain"realtime"timebound,almostalwayslessthan5to10seconds.(b)MainMemoryDatabase:Microseconds/secondsqueryresponserestrictionsnecessitatemain-memory-onlydatabases.(c)ScalableDatabase:OncetheenvironmentofaPLCandtherequirementsoftheassociatedapplicationprogramaredetermined,thepossiblequerytypestothedatabasestayfixedforareasonablylongperiodoftime.Sincetheresponsetimeofqueriesisofutmostimportance,theDBMSshouldbescaledsothatonlytheneededroutines/functions(e.g.,accessmethods,datastructures,etc.)areincorporated.Insection2,wediscussthegeneralcharacteristicsPLCs,andbrieflypresenttheladderlogiclanguage.Section3discussesthefeaturesoftheproposeddatabasesystemforPLCs.Ingeneral,thePLChardwareismostlycustom-builtwithoccasionaloff-the-shelfhardware,andconsistsofaCPU(ormultipleCPUs),mainmemory,an"industrialterminal",andhigh-andmedium-speeddatacommunicationshardware.Thesizeofthemainmemoryrangesfrom16Kbytes(of5to10yearsago)to8Mbytes(ofthepresenttime).AlthoughtheCPUhasaninstructionsetsimilartothosefoundinCPUsof16-bitand32-bitmachines,itisespeciallyequippedwithfastbitmanipulationinstructions.TheindustrialterminalcomeswithaspecialkeyboardtomaketheprogrammingofthePLCeasierand/ortointervenewiththeapplicationprogram.ThePLCsoftwareconsistsofanoperatingsystem(rangingfromaverysimplisticmonitor(oftenyearsago)toasophisticatedreal-timeoperatingsystem(oftherecenttime)),high-speedcommunicationssoftwareforcommunicatingwithI/Oprocessors,medium-speedcommunicationssoftwaretotheindustrialterminalandtoother"intelligent"devices.Bothgeneral-purposecomputersandPLCsareusedforindustrialcontrol[Star87].However,theydifferintheprogramminglanguagesthattheyuse,environmentalspecifications,andtheirusertypes.PLCsarerugged,andworkinhostileenvironmentswithnospecialclimatecontrols,toleratingextremesoftemperature(60°C),humidity(95%)andaircontamination.UsersofPLCsincludetheoriginalprogrammersoftheapplicationprograms,aswellasplantelectriciansandmaintenancepersonnel,whoareaccustomedtorelay-typecontrollingenvironments.ArungisanorderedsetofPLCinstructionsdrawnonasingleline.Instructionsonarungareclassifiedasinputinstructions(thosethatmonitortheinputbuffer)andoutputinstructions(thosethatsettheoutputbuffer),andareexecutedfromlefttoright,sequentially(Pleaseseefigure4).APLCapplicationprogramconsistsofamainprogramandasetofsubroutines,eachofwhichcontaininganorderedsetofrungs。Tosummarize,theapplicationprogrammerdealswithactual(realtime)clocktimes,andneedstohavepreciseestimatesforprogramscantimesandI/Oscantimes.Fortimeestimations,thePLCmanufacturerssupplyinformationsuchas4msecondsfor1000ladderlogicinstructions,and1msecondsforcopying256wordsintoaninputbufferduringtheI/Oscan.Inmostapplications,theprocessorscantimeiskeptbelow10seconds.Thus,databasemanipulationinstructionsalsoneedtohaveprecisetimelimitsavailableto(orsetby)users.2.ArchitectureWeproposeatwo-level,single-userdatabasesystemarchitectureasshowninfigure6.WehaveomittedfromourarchitecturetheexternalmodelofthetraditionaldatabasearchitecturenotbecausePLCsarenotpowerful,butbecauseconcurrentlyrunningapplicationprogramsusingdifferentviewscreateproblemsinaccuratelyestimatingtheapplicationprogramscantimes.Thatis,inamultitaskingenvironmentwheretaskscompetefortheresourcessuchasdatabaserelationsandcommunicationlines,decidingasingletop-tobottomexecutiontimeofataskinactualtimeisratherdifficult(ifatallpossible).Asfarasthehardwarecomputingpowerisconcerned,thepresentdayPLCsareaspowerfulaspersonalcomputers(and,indeed,insomerecentproducts,PLCsarepersonalcomputers),andcancertainlysupportmultipleindustrialterminalsanddatasharingamongtheapplicationprograms.3.DataModelingIssuesThetraditionaldatamodelingtechniquesdirectlyapplytoPLCdatabases.Thereisnoreasonwhy,say,theEntity-RelationshipModel[Chen76]ofthedatainthePLCdatabasecannotbedesigned.Allthewell-knownadvantagesofdatamodeling[ToeF82]directlycarryovertothePLCdatabaseenvironment,andwillnotbeelaboratedhere.Asfortheconceptualmodelofourprototypeeffort,wehavechosentherelationalmodel.ThePLCenvironmentnaturallydealswithhistoricaldata,e.g.,thelastreadingofagrindingmachinesensor,itsvalueyesterday,etc..Again,therearevarioushistoricaldatamodelingapproaches[SnoA85]intheliteratureand,theoretically,anyoneofthemisacceptable.Example.Considerasetoffurnacesthatproducehigh-precisionairplaneparts.Therearetwoentityrelations,FURNACEandPART,andonetime-varyingrelationshiprelationPRODUCESasdescribedinfigure7.PleasenotethatPRODUCESrelationhastupletimestampingwithBEGIN-TIMEandEND-TIMEattributes.4.DBMSIssuesThereareanumberofissuesthatneedtoberesolvedinatime-constrained,singleuserDBMSenvironment.Theseare(a)DataArchival.(b)DatabaseBackup.(c)DatabaseIntegrityenforcement.5.QueryProcessingIssuesTheconventionaldatabasemanagementsystems(DBMS)donothavethecapabilityofdynamicallymeetingthetimeconstraintswhentheamountofdataistoolargetoprocesswithinagiventimequota.Ourapproachis,foragiventimequota,totakeanappropriateamountofsampledatasuchthatthesetofsampleddataisguaranteedtobeprocessiblebytheDBMSwithinthegiven.SomebasicPLCinstructionshavealsobeenextendedtoincreasetheirfunctionality.Forexample,wehaveextendedthe"examinelogicswitch"instructions,theExamineInputClosed(XIC)andtheExamineInputOpen(XIO)[AB84,AB85],totestthelogicalvalueofapropositionalcalculusformula,ratherthantestingabitvaluecorrespondingtotheconditionofaphysicalI/O.An"examineF"instructioncausestheformulaFtobeevaluatedandtherolevalueisthenexaminedasinthebasicexamineinstructions.Ingeneral,theformulaFmaycontainaconstant,avariable,acomponentofatuplebeingscannedbythepointer,andfiE)wherefisanaggregatefunctionandEisarelationalalgebraexpression.ThefunctionalityofthePLCTimerandCounterinstructionshavealsobeenenhanced.Usuallyconditionedby"examine"instructions,timersandcounterskeeptrackoftimedintervalsorevents;thenumberoftimedintervalsoreventstobecountedissetinthepresetvaluevariables[AB85,AB84].Withtheintroductionofatimedimensionintothedatabase,eventsandintervalscanalsobe"counted"usingdatabasequeries.6.QueryProcessingIssuesTheconventionaldatabasemanagementsystems(DBMS)donothavethecapabilityofdynamicallymeetingthetimeconstraintswhentheamountofdataistoolargetoprocesswithinagiventimequota.Ourapproachis,foragiventimequota,totakeanappropriateamountofsampledatasuchthatthesetofsampleddataisguaranteedtobeprocessiblebytheDBMSwithinthegiventimequota,and,exacttime-costformulascanbederived.Clearly,themorestagesthequeryprocessorgoesthrough,themoreoverheadisinvolvedintherun-timeestimationapproach.Thisimpliesthat,ateachstage,aslargeanamountoftimeaspossibleshouldbeallocatedtoreducethenumberofstages.Ontheotherhand,allocatinglargeamountsoftimehasahigherriskofoverspendingthetimequotaandmayendupwastingalargeamountoftime,especiallyinahardtimeconstrainedenvironment[AbGM88,StZa88].Thehardtimeconstrainedenvironmentsdenotethoseenvironmentswhereoverspendingthetimequotaisstrictlynotallowed.Therefore,whenoverspendinghappens,thequeryhastobeabortedprematurelyandtheamountoftimeusedinthelaststageisconsideredwasted.7.OtherIssuesTheissueofincompleteinformationinthePLCdatabaseisalsobeinginvestigated.Quiteoften,thesensorsgiveincompleteinformation,usuallyarangeforareading.Onthoseoccasions,theincompletedataisonlyknowntobewithinsomerangeofvalues.Werepresentanincompletedataitemasanintervalwhichcontainstheunknownvalue.WehavefinishedtheimplementationofthefirstversionofaPLCdatabase[-Liu89]havingsomeofthefeaturessummarizedinsection3.ThesystemhasbeendevelopedonSUNworkstationsusingtheClanguage.WeareplanningtotransportitintoaPLC,andevaluateitsperformance.References[AB84]PLC-3ProgrammableControllerProgrammingManual,Allen-BradleyCo.,1984.[AB85]PLC-5/15ProgrammableControllerProcessorManual,Allen-BradleyCo.,1985.[Chri83]Christodoulakis,S.,"EstimatingRecordSelectivities",InformationSystems,Vol8,1983.[HP88]Hewlett-PackardAnnouncementoftheHPRTDBS,Sept.1988.[Klug81]A.Klug,"ABE-AQueryLanguageforConstructingAggregate-by-Example",1stLBLWorkshoponStatisticalDatabaseManagement,Dec.1981.[Ullm88]J.DUllman,"PrinciplesofDatabaseandKnowledge-BaseSystems",ComputerSciencePress,1988.[SSDB86]PanelonScientificDatabases,ThirdInt.WorkshoponStatisticalandSCientificDatabaseManagement,1986.[Star87]R.J.Staron,"AToolsettoDevelopProgrammableControllerSystems",unpublishedmanuscript,Allen-BradleyCo.,March1987.

可編程控制器的數(shù)據(jù)庫系統(tǒng)文章摘要在這篇文章中，我們確定一種在科學(xué)和工業(yè)上有分外應(yīng)用目的的計算機——可編程控制器(PLC)數(shù)據(jù)庫系統(tǒng)的相關(guān)問題。例如：在制造環(huán)境的工廠里。我們建議作為數(shù)據(jù)庫系統(tǒng)的PLC的那些單用戶，實時可調(diào)整的主記憶體。只有關(guān)系數(shù)據(jù)庫系統(tǒng)有一個雙級結(jié)構(gòu)，具有歷史數(shù)據(jù)建模和操作能力，查詢處理技術(shù)。區(qū)別于階梯邏輯語言，最常用的PLC語言，融合數(shù)據(jù)操作語言指令。我們放入一個單獨組成的PLC處理器的掃描時間，處理數(shù)據(jù)庫更新，備份簡單算法和數(shù)據(jù)檔案等問題。1.簡介可編程控制器(PLC)是一個專用計算機,用來實施科學(xué)計算系統(tǒng)和工業(yè)控制系統(tǒng)。在本文中舉一個自動化控制工廠的機器運行的例子。本文是一份立場文章，提出了PLC的數(shù)據(jù)庫系統(tǒng),并討論其特征。這樣，我們接觸基地的一批基礎(chǔ)數(shù)據(jù)庫,因為經(jīng)常提及其他工作細節(jié)而使內(nèi)容很豐富?？删庈壏犊刂破鞔蠖嘤糜谥圃斓沫h(huán)境，所以我們選擇了運行的例子。不過，也有的可編軌范控制器用在科學(xué)應(yīng)用的信號數(shù)據(jù)采集和初步數(shù)據(jù)處理。因此，我們認為對一些科學(xué)應(yīng)用，可編程數(shù)據(jù)庫,也可以作為本地較大的科學(xué)數(shù)據(jù)庫的瞬態(tài)部分?，F(xiàn)在我們列出有一個直接內(nèi)置數(shù)據(jù)庫系統(tǒng)的PLC的優(yōu)點。(1)數(shù)據(jù)建模技術(shù)：輸入和輸出緩沖器是一個對真實世界的活動比力散亂的暫態(tài)模型，因此，卡爾建模法是傳統(tǒng)數(shù)據(jù)庫建模技術(shù)中比力好的方式。(2)歷史數(shù)據(jù)庫：可編軌范控制器一段時間內(nèi)例行處理分歧版本的數(shù)據(jù)。因此，歷史數(shù)據(jù)建模技術(shù)以及歷史數(shù)據(jù)把持技術(shù)可以取代專案方式把持的歷史數(shù)據(jù)的可編軌范控制器。(3)用戶界面友愛：目前在市場上買到的該PLC的軟件。能有限的展示信息和可變數(shù)據(jù)信息存儲。例如，接觸直方圖顯示功能作為開機/關(guān)機史上的一個特定的主記憶體。(4)處理大量數(shù)據(jù)：由于一個數(shù)據(jù)庫和查詢語言的增加，PLC能夠分析大容量數(shù)據(jù)。(5)在PLC水平上的數(shù)據(jù)壓縮和壓實：目前，由簡單系統(tǒng)或是簡單處理的的信息，收集的數(shù)據(jù)由PLC的傳送并儲存到主機的內(nèi)存中。由于目前的可編軌范控制器不能分析出令人滿意的大部分的數(shù)據(jù)，而只是將數(shù)據(jù)傳輸?shù)街鳈C。在一些科學(xué)實驗和應(yīng)用中，需要收集到的數(shù)據(jù)是如此之大?，F(xiàn)在還沒有PLC的數(shù)據(jù)庫和實時數(shù)據(jù)庫的書面文獻報道。然而，就在比來，惠普頒布頒布了1989年獲得惠普實時數(shù)據(jù)庫[惠普88]所用的內(nèi)部結(jié)構(gòu)。顯然，結(jié)構(gòu)圖3的主機通信線路勝于結(jié)構(gòu)。然而，個人電腦可能超載太大都據(jù)。現(xiàn)在我們開始討論可編程數(shù)據(jù)庫的性能。(1)實時數(shù)據(jù)庫：相當短的“實時”一般從微秒到秒，數(shù)據(jù)的輸入緩沖器必需經(jīng)過掃描。因此,對查詢必需包管其將低于必然的“實時”。有時限的，幾乎總是低于5至10秒。(2)內(nèi)存數(shù)據(jù)庫:查詢響應(yīng)限制必需的主內(nèi)存只有數(shù)據(jù)庫。(3)分級數(shù)據(jù)庫：一旦PLC的環(huán)境和要求的相關(guān)應(yīng)用軌范被決意，相當長的時期就留在一個固定的可能的查詢類型的數(shù)據(jù)庫中。由于響應(yīng)時間的問題是至關(guān)重要的，該數(shù)據(jù)庫應(yīng)該加碼,所需要常規(guī)本能機能(例如，檢索方式，數(shù)據(jù)結(jié)構(gòu)等)都可以納入傍邊。接下來，我們討論可編軌范控制器的特點，并簡要地介紹了梯形圖語言。就第三節(jié)討論的特點,提出了可編程控制器的數(shù)據(jù)庫系統(tǒng)。2PLC和梯形圖語言的一般特征在一般情況下，PLC的硬件大多是量身訂做的。偶爾現(xiàn)成的硬件，則由一個CPU(或多個中央處理器)，內(nèi)存，“產(chǎn)業(yè)終端”而組成高、中速數(shù)據(jù)通信硬件組成復(fù)雜的內(nèi)存容量，16k字節(jié)(5至10年前)8兆字節(jié)(當前時間)。雖然CPU有一個指令集類似CPU的16位和32位機。它分外配備了快速位操作指令。工業(yè)終端是一個特殊鍵盤使編程的PLC容易融合應(yīng)用程式。該PLC的軟件包孕操作系統(tǒng)(從一個非常簡單的監(jiān)控器(