信息系統(tǒng)外文文獻(xiàn)翻譯---系統(tǒng)的分析與設(shè)計(jì)

1、 I附錄1外文翻譯（原文）SystemsAnalysisandDesignWorkingundercontrolofastoredprogram,acomputerprocessesdataintoinformation.Thinkaboutthatdefinitionforaminute.Anygivencomputerapplicationinvolvesatleastthreecomponents:hardware,software,anddata.Merelywritingaprogramisntenough;becausetheprogramisbutonecomponentinas

2、ystem.Asystemisagroupofcomponentsthatworktogethertoaccomplishanobjective.Forexample,considerapayrollsystem.Itsobjectiveispayingemployees.Whatcomponentsareinvolved?Eachday,employeesrecordtheirhoursworkedontimecards.Attheendofeachweek,thetimecardsarecollectedanddeliveredtothecomputercenter,wheretheyar

3、ereadintoapayrollprogram.Asitruns,theprogramaccessesdatafiles.Finally,thepaychecksareprintedanddistributed.Forthesystemtowork,people,procedures,inputandoutputmedia,files,hardware,andsoftwaremustbecarefullycoordinated.Notethattheprogramisbutonecomponentinasystem.Computer-basedsystemsaredevelopedbecau

4、sepeopleneedinformation.Thosepeople,calledusers,generallyknowwhatisrequired,butmaylacktheexpertisetoobtainit.Technicalprofessionals,suchasprogrammers,havetheexpertise,butmaylacktrainingintheusersfield.Tocomplicatematters,usersandprogrammersoftenseemtospeakdifferentlanguages,leadingtocommunicationpro

5、blems.Asystemsanalystisaprofessionalwhotranslatesuserneedsintotechnicalterms,thusservingasabridgebetweenusersandtechnicalprofessionals.Likeanengineeroranarchitect,asystemsanalystsolvesproblemsbycombiningsolidtechnicalskillswithinsight,imagination,andatouchofart.Generally,theanalystfollowsawell-defin

6、ed,methodicalprocessthatincludesatleastthefollowingsteps;ProblemdefinitionAnalysisDesign.Implementation5.MaintenanceAttheendofeachstep,resultsaredocumentedandsharedwithboththeuserandtheprogrammers.Theideaistocatchandcorrecterrorsandmisunderstandingsasearlyaspossible.Perhapsthebestwaytoillustratethep

7、rocessisthroughexample.Pictureasmallclothingstorethatpurchasesmerchandiseatwholesale,displaysthisstock,andsellsittocustomersatretail.Ontheonehand,toomuchstockrepresentsanunnecessaryexpense.Ontheotherhand,apoorselectiondiscouragesshoppers.Ideally,abalancecanbeachieved:enough,butnottoomuch.Complicatin

8、gmattersisthefactthatinventoryisconstantlychanging,withcustomerpurchasesdepletingstock,andreturnsandreordersaddingtoit.1Theownerwouldliketotrackinventorylevelsandreorderandgivenitemjustbeforethestorerunsout.Forasingleitem,thetaskiseasy-justcountthestock-on-hand.Unfortunately,thestorehashundredsofdif

9、ferentitems,andkeepingtrackofeachoneisimpractical.Perhapsacomputermighthelp.2-1ProblemDefinitionThefirststepinthesystemsanalysisanddesignprocessisproblemdefinition.Theanalystsobjectiveisdeterminingwhattheuser(inthiscase,thestoresowner)needs.Notethat,astheprocessbegins,theuserpossessesthecriticalinfo

10、rmation,andtheanalystmustlistenandlearn.Fewusersaretechnicalexperts.Mostseethecomputerasamagicbox,andarenotconcernedwithhowitworks.Atthisstage,theanalysthasnobusinesseventhinkingaboutprograms,files,andcomputerhardware,butmustcommunicatewiththeuseronhisorherownterm.Theideaistoensurethatboththeuserand

11、theanalystarethinkingaboutthesamething-Thus,aclear,writtenstatementexpressingtheanalystsunderstandingoftheproblemisessential.Theusershouldreviewandcorrectthiswrittenstatement.Thetimetocatchmisunderstandingsandoversightsisnow,beforetime,moneyandeffortarewasted.Often,followingapreliminaryproblemdefini

12、tion,theanalystperformsafeasibilitystudy.Thestudyabriefcapsuleversionoftheentiresystemsanalysisanddesignprocess,attemptstoanswerthreequestions:Cantheproblembesolved?Canitbesalvedintheusersenvironment?Canitbesolvedatareasonablecost?Iftheanswertoanyoneofthesequestionsisno,thesystemshouldnotbedeveloped

13、.Givenagoodproblemdefinitionandapositivefeasibilitystudy,theanalystcanturntoplanninganddevelopingaproblemsolution.2-2AnalysisAsanalysisbegins,theanalystunderstandstheproblem.Thenextstepisdeterminingwhatmustbedonetosolveit.Theuserknowswhatmustbedone1duringanalysis;thisknowledgeisextractedandformallyd

14、ocumented.Mostusersthinkintermsofthefunctionstobeperformedandthedataelementstobemanipulated.Theobjectiveistoidentifyandlinkthesekeyfunctionsanddataelements,yieldingalogicalsystemdesign.Startwiththesystemsbasicfunctions.Thekeyiskeepingtrackofthestock-on-handforeachproductininventory.Inventorychangesb

15、ecausecustomerspurchase,exchange,andreturnproducts,sothesystemwillhavetoprocesscustomertransactions.Thestoresownerwantstoselectivelylookattheinventorylevelforanyproductinshortsupplyand,ifappropriate,orderreplacementstock,sothesystemmustbeabletocommunicatewithmanagement.Finally,followingmanagementaut

16、horization,thesystemshouldgenerateareorderreadytosendtoasupplier.DatasourceordestinationProcessthattransformsdatastoreDatallawFig1Giventhesystemsbasicfunctions,theanalystsnexttaskisgainingasenseoftheirlogicalrelationship.Agoodwaytostartisbydescribinghowdataflowbetweenthefunctions.Asthenameimplies,da

17、taflowdiagramsareparticularlyusefulforgraphicallydescribingthesedataflows.Foursymbolsareused(Fig.1).Datasourcesanddestinationsarerepresentedbysquares;inputdataenterthesystemfromasource,andoutputdataflowtoadestination.Onceinthesystem,thedataaremanipulatedorchangebyprocesses,representedbyround-cornerr

18、ectangles.Aprocessmightbeaprogram,aprocedure,oranythingelsethatchangesormovesdata.Datacanbeheldforlaterprocessingindatastores,symbolizedbyopen-endedrectangles.Adatastoremightbeadiskfile,atapefile,adatabase,writtennotes,orevenapersonsmemory.Finally,dataflowbetweensources,destinations,processes,enddat

19、astoresoverdataflows,whicharerepresentedbyarrows.Fig2Figure2showsapreliminarydataflowdiagramfortheinventorysystem.StartwithCUSTOMER.Transactionsflowfromacustomerfintothesystem,wheretheyarehandledbyProcesstransaction.Adatastore,STOCK,holdsdataoneachitemininventory.Processtransactionchangesthedatatore

20、flectthenewtransaction.Meanwhile,MANAGEMENTaccessesthesystemthroughCommunicate,evaluatingthedatainSTOCKand,ifnecessary,requestingareorder.Once,areorderisauthorized.GeneratereordersendsnecessarydatatotheSUPPLIER,whoshipstheitemstothestore.Notethat,becausethereorderrepresentsachangeintheinventorylevel

21、ofaparticularproductorproductsitishandledasatransaction.Thedataflowdiagramdescribesthelogicalsystem.Thenextstepistracingthedataflows.StartwiththedestinationSUPPLIER.Reordersflowtosuppliers;forexample,thestoremightwant25pairsofjeans.Tofilltheorder,thesupplierneedstheproductdescriptionandthereorderqua

22、ntity.Wheredothesedataelementscomefrom?SincetheyareoutputbyGeneratereorder,theymusteitherbeInputtoorgeneratedbythisprocess.DataflowintoGeneratereorderforSTOCK;thus,productdescriptionsandreorderquantitiesmustbestoredinSTOCK.Otherdataelements,suchastheitempurchasedandthepurchasequantityaregeneratedbyC

23、USTOMER.Stillothers,forexamplesellingpriceandreorderpoint,aregeneratedbyorneededbyMANAGEMENT.Thecurrentstock-on-handforagivenitemisanexampleofadataelementgeneratedbyanalgorithminoneoftheprocedures.Stepbystep,methodically,theanalystidentifiesthedataelementstobeinputto.storedby,manipulatedby,generated

24、by,oroutputbythesystem.Tokeeptrackofthedataelements,theanalystmightlisteachoneinadatadictionary.Asimpledatadictionarycanbesetuponindexcards,butcomputerizeddatadictionarieshavebecomeincreasinglypopular.Thedatadictionary,acollectionofdatadescribinganddefiningthedata,isusefulthroughoutthesystemsanalysi

25、sanddesignprocess,andisoftenusedtobuildadatabaseduringtheimplementationstage.Theideaofanalysisistodefinethesystemsmajorfunctionsanddataelementsmethodically.Rememberthattheobjectiveistranslatinguserneedsintotechnicalterms.Sincethesystemstartswiththeuser,thefirststepisdefiningtheusersneeds.Usersthinki

26、ntermsoffunctionsanddata.Theydonotvisualizeprograms,orfiles,orhardware.andduringthisinitial,crucialanalysisstageitisessentialthattheanalystthinklikeauser,notlikeaprogrammer.Dataflowdiagramsanddatadictionariesareusefultools.Theyprovideaformatforrecordingkeyinformationabouttheproposedsystem.Also,theyj

27、ogtheanalystsmemory)forexample,訐theanalystdoesnthavesufficientinformationtocompleteadatadictionaryentry,heorshehasprobablymissedsomething.Perhapsmostimportantly,thedataflowdiagramandthedatadictionarydocumenttheanalystsunderstandingofthesystemrequirements.Byreviewingthesedocuments,theusercancorrectmi

28、sunderstandingsoroversights.Finally,theyrepresentanexcellentstartingpointthenextstep,design.2-3DesignAsweenterthedesignstage,weknowwhatthesystemmustdo,andthuscanbeginthinkingabouthowtodoit.Theobjectiveistodevelopastrategyforsolvingtheproblem.Atthisstage,wearenotinterestedinwritingcodeorindefiningpre

29、cisedatastructures;instead,wewanttoidentify,atablackboxlevel,necessaryprograms,files,procedures,andothercomponents.Thedataflowdiagramdefinesthesystemsnecessaryfunctions;howmighttheybeimplemented?Onepossibilityiswritingoneprogramforeachprocess.Anotheriscombiningtwoormoreprocessesinasingleprogram;ther

30、earedozensofalternativesolutions.Letsfocusononeoptionanddocumentit.Asystemflowchartusessymbolstorepresentprograms,procedures,hardwaredevices,andtheothercomponentsofaphysicalsystem(Fig.3).Ourflowchart(.Fig.4)showsthattransactiondataenterthesystemthroughaterminal,areprocessedbyadatacollectionprogram,a

31、ndthenarestoredonaninventoryfile.Eventually,theinventoryfileisprocessedbyaReportandreorderprogram.Throughit,managementmanipulatesthedataandauthorizesreorders.Fig.4onasystemflowchart,symbolsrepresentprograms,procedures,hardwaredevices,andtheothercomponentsofaphysicalsystem.Programorf(Magneticprocedur

32、edrumPunchedcardaDisplayPrintedoutput二ManuafinputMagnetictapeV7ManualprocessOnlinestorageConununlcationlinkMagneticdiskCDTerminalpointFig3Lookatthesystemflowchart.Itidentifiesseveralhardwarecomponents,includingacomputer,adiskdrive,adataentryterminal,aprinter,andadisplayterminal.Twoprogramsareneeded;

33、ProcesstransactionandReportandreorder.Inadditiontothehardwareandtheprograms,wellneeddatastructuresfortheinventoryfileandfordataflawsbetweentheI/Odevicesandthesoftware.Notethatthissystemflowchartillustratesonepossiblesolution;agoodanalystwilldevelopseveralfeasiblealternativesbeforechoosingone.Fig4The

34、flowchartmapsthesystem,highlightingitsmajorphysicalcomponents.Sincethedatalinkthecomponents,thenexttaskisdefiningthedatastructures.Consider,forexample,theinventoryfile.ItcontainsallthedataelementsfromthedatastoreSTOCK.Thedataelementsarelistedinthedatadictionary.Usingthem,thefilesdatastructurecanbepl

35、anned,Howshouldthefilebeorganized?Thatdependsonhowitwillbeaccessed.Forexample,insomeapplications,dataareprocessedatregular,predictableintervals.Typically,thedataarecollectedovertimeandprocessedtogether,asabatch.Ifbatchprocessingisacceptable,asequentialfileorganizationisprobablybest.Itisnotalwaysposs

36、ibletowaituntilabatchoftransactionsiscollected,however.Forexample,consideranairdefenseearlywarningsystem.Ifanunidentifiedaircraftisspotteditmustbeidentifiedimmediatelytheideaofwaitinguntil5_00p.m.becausethatswhentheairdefenseprogramisrunisabsurd.Instead,becauseoftheneedforquickresponse,eachtransacti

37、onmustbeprocessedasitoccurs.Generallysuchtransactionprocessingsystemscallfordirectaccessfile.Ourinventorysystemhastwoprograms.Oneprocessestransactions.Adirectaccessinventoryfileseemsareasonablechoice.Theotherallowsmanagementtostudyinventorydataoccasionally;batchprocessingwouldcertainlydo.Shouldthein

38、ventoryfilebeorganizedsequentiallyordirectly?Facedwithsuchachoiceagoodanalystconsidersbothoptions.Onepossiblesystemmightaccepttransactionsandprocessthemastheyoccur.Asanalternative,salesslipsmightbecollectedthroughoutthedayandprocessedasabatchafterthestorecloses.Inthefirstsystem,thetwoprogramswouldde

39、alwithdirectaccessfiles;inthesecondsystem,theywouldbelinkedtosequentialfiles.Aprogramtoprocessdirectaccessdataisdifferentfromaprogramtoprocesssequentialdata.Thedatadrivethesystem.Thechoiceofadatastrueturedeterminestheprogramsstrueture.Notethattheprogramdefinedandplannedinthecontextofthesystem.2-4Imp

40、lementationOncethesystemsmajorcomponentshavebeenidentified.wecanbegintodevelopthem.Oursystemincludestwoprograms,severalpiecesofequipment,andanumberofdatastructures.Duringimplementation,eachprogramisplannedandwrittenusingthetechniquesdescribedinChapter7.Filesarecreated,andtheircontentschecked.Newhard

41、wareispurchased,installed,andtested.Additionally,operatingproceduresarewrittenandevaluated.Onceallthecomponentpartsareready,thesystemistested.Assumingtheuserissatisfied,thefinishedsystemisreleased.2-5MaintenanceMaintenancebeginsafterthesystemisreleased.Aspeopleuseit,theywillsuggestminorimprovementsa

42、ndenhancements.Occasionally,bugsslipthroughdebugandtesting,andremovingthemisanothermaintenancetask.Finally,conditionschange,andaprogrammustbeupdated;forexample,ifthegovernmentpassesalowchangingtheprocedureforcollectingincometaxes,thepayrollprogrammustbemodified.Maintenancecontinuesforthelifeofasyste

43、m,anditscostcaneasilymatchorexceedtheoriginaldevelopmentcost.Goodplanning,soliddocumentation,andwell-structuredprogramscanhelptominimizemaintenancecost.附錄2外文翻譯（譯文）系統(tǒng)的分析與設(shè)計(jì)在存儲(chǔ)程序的控制下，計(jì)算機(jī)把數(shù)據(jù)處理成信息。對(duì)系統(tǒng)的定義略加思考，任何一個(gè)已知的計(jì)算機(jī)應(yīng)用至少包含三個(gè)部分，硬件、軟件和數(shù)據(jù)。僅僅編寫(xiě)一個(gè)程序是不夠的，因?yàn)槌绦蛑皇窍到y(tǒng)中的一部分。系統(tǒng)就是為實(shí)現(xiàn)一個(gè)目標(biāo)而共同工作的一組部件。例如，考慮一個(gè)工資系統(tǒng)，它的目標(biāo)是

44、為雇員付工資，應(yīng)包含哪幾部分呢？每天雇員們把他們工作的時(shí)數(shù)記錄在計(jì)時(shí)卡片上，每周末把計(jì)時(shí)卡片收集起來(lái)，送給計(jì)算中心，在計(jì)算中心把計(jì)時(shí)卡片上的數(shù)據(jù)讀給工資程序。當(dāng)工資程序執(zhí)行時(shí)，程序存取數(shù)據(jù)文件。最后，打印出工資單，用來(lái)分發(fā)。為使系統(tǒng)工作，人、處理過(guò)程、輸入和輸出介質(zhì)、文件、硬件和軟件都必須認(rèn)真地協(xié)調(diào)。注意，程序只是系統(tǒng)中的一部分。因?yàn)槿藗冃枰畔?，所以要開(kāi)發(fā)基于計(jì)算機(jī)的系統(tǒng)。被稱(chēng)為用戶(hù)的那些人常常知道需求什么信息，但是他們可能缺乏得到這些信息的計(jì)算機(jī)的專(zhuān)門(mén)知識(shí)。計(jì)算機(jī)技術(shù)方面的專(zhuān)業(yè)人員，例如程序設(shè)計(jì)員有這方面的專(zhuān)門(mén)知識(shí)，但是可能在用戶(hù)的專(zhuān)業(yè)領(lǐng)域內(nèi)缺少訓(xùn)練。麻煩的是。用戶(hù)和程序員似乎常常講不同的

45、語(yǔ)言，導(dǎo)致了兩者之間的聯(lián)系障礙。系統(tǒng)分析員是一個(gè)專(zhuān)業(yè)人員，他能把用戶(hù)的需求轉(zhuǎn)換成計(jì)算機(jī)技術(shù)術(shù)語(yǔ)。因此他是用戶(hù)和技術(shù)專(zhuān)業(yè)人員之間的橋梁。像工程師或建筑師一樣，系統(tǒng)分析員把他扎實(shí)的技術(shù)技能與知識(shí)、想象力和一點(diǎn)藝術(shù)結(jié)合起來(lái)去解決問(wèn)題通常，分析員遵循一個(gè)意義明確的有條理的過(guò)程，至少應(yīng)包括以下幾個(gè)步驟：?jiǎn)栴}的定義分析設(shè)計(jì)實(shí)現(xiàn)維護(hù)在每一步驟的結(jié)尾，研究的結(jié)果都要形成文件，提供給用戶(hù)和程序設(shè)計(jì)員?；镜乃枷胧且M早地抓住和修正錯(cuò)誤以及一些未理解之處。也許通過(guò)一個(gè)例子來(lái)說(shuō)明該過(guò)程是最好的方法。設(shè)想一個(gè)小服裝店，成批地購(gòu)買(mǎi)貨物，把貨物擺在貨架上，零售給顧客。一方面庫(kù)存太多會(huì)造成不必要的開(kāi)銷(xiāo)；另一方面可供挑選的商

46、品太少會(huì)使顧客失去購(gòu)買(mǎi)的信心。理想上，希望達(dá)到一個(gè)平衡，貨物即充足但又不太多。麻煩的是，隨著顧客的購(gòu)買(mǎi)庫(kù)存減少了，還有退貨以及追加訂貨等情況，所以貨物的清單經(jīng)常地發(fā)生變化店主喜歡按貨物清單購(gòu)銷(xiāo)，剛好在商店售完某種貨物之前，再訂購(gòu)這種貨。對(duì)一項(xiàng)商品，該任務(wù)是容易完成的，只要計(jì)算一下手頭現(xiàn)存的貨物數(shù)量就行了。遺憾的是商店要經(jīng)管幾百種不同的貨物，始終跟蹤每一種貨物的銷(xiāo)售情況是不實(shí)際的，也許計(jì)算機(jī)可以幫這個(gè)忙吧！2.1問(wèn)題定義在系統(tǒng)分析和設(shè)計(jì)過(guò)程中的第一步，是問(wèn)題的定義。分析員的目標(biāo)是確定用戶(hù)需求什么（本例中就是店主需求什么）。注意，當(dāng)這個(gè)過(guò)程開(kāi)始時(shí)，用戶(hù)擁有很重要的資料，分析員必須認(rèn)真地聽(tīng)和學(xué)。用戶(hù)

47、幾乎都不是計(jì)算機(jī)方面的專(zhuān)家，他們大多數(shù)人把計(jì)算機(jī)看成魔術(shù)盒，并不關(guān)心它是如何工作的。在該階段上，分析員不必考慮程序、文件或計(jì)算機(jī)硬件，但他們必須用自己的專(zhuān)業(yè)術(shù)語(yǔ)與用戶(hù)對(duì)話(huà)。目的是確保用戶(hù)和分析員兩者都思考同一件事。因此，一份能表達(dá)分析員對(duì)問(wèn)題理解程度的清晰的書(shū)面報(bào)告是必要的。用戶(hù)應(yīng)該反復(fù)地閱讀和修改這份書(shū)面報(bào)告。此時(shí)是在時(shí)間、金錢(qián)和精力被浪費(fèi)之前抓出錯(cuò)誤和疏漏的好時(shí)機(jī)。通常，接著初步的問(wèn)題定義，分析員要進(jìn)行可行性研究。該研究是整個(gè)系統(tǒng)分析和設(shè)計(jì)的一個(gè)簡(jiǎn)略的方案，應(yīng)力圖回答以下三個(gè)問(wèn)題：?jiǎn)栴}能解決嗎？在用戶(hù)的環(huán)境下問(wèn)題能解決嗎？在一個(gè)合適的花費(fèi)上問(wèn)題能解決嗎？如果這些問(wèn)題中的任何一個(gè)得到的是否定

48、回答，那么該系統(tǒng)就不應(yīng)開(kāi)發(fā)。有了好的問(wèn)題定義和肯定的可行性研究，分析員就能著手計(jì)劃和研究問(wèn)題的解了。2.2分析分析開(kāi)始時(shí)，分析員要理解問(wèn)題，下一步要決定的是為了解決問(wèn)題必須做什么。用戶(hù)清楚必須做什么。在分析階段礙到了這方面知識(shí)，并正式地形成文件。大多數(shù)用戶(hù)是按著所要完成的功能和所要處理的數(shù)據(jù)元素去思考的，目的是要區(qū)分并聯(lián)接這些關(guān)鍵的功能和數(shù)據(jù)元素，隨之產(chǎn)生邏輯系統(tǒng)設(shè)計(jì)。從系統(tǒng)的基本功能入手，關(guān)鍵是始終監(jiān)視貨單中每種商品的現(xiàn)存量。因?yàn)轭櫩唾?gòu)買(mǎi)、換貨和退貨，所以貨單要改變，因此系統(tǒng)必須處理顧客辦理的手續(xù)。店主希望有選擇地查看供應(yīng)中任意一種短缺商品的清單，如果合理的話(huà)，定貨補(bǔ)充庫(kù)存，因此系統(tǒng)必須能和

49、經(jīng)營(yíng)管理部門(mén)對(duì)話(huà)。最后，經(jīng)過(guò)經(jīng)營(yíng)管理部門(mén)的核準(zhǔn)，系統(tǒng)應(yīng)該產(chǎn)生一個(gè)重新訂貨單，準(zhǔn)備發(fā)送給供應(yīng)商。已知了系統(tǒng)的基本功能，分析員的下一個(gè)任務(wù)是分析理解這些功能之間邏輯關(guān)系的知識(shí)。啟動(dòng)這項(xiàng)工作的一個(gè)好方法是描述功能之間的數(shù)據(jù)如何流動(dòng)顧名思義，為了用圖解方法描述這些數(shù)據(jù)流，那么數(shù)據(jù)流程圖就是特別有用的圖1中用到四種符號(hào)數(shù)據(jù)的像和目的地用方框表示，輸入的數(shù)據(jù)從源進(jìn)入系統(tǒng)，而輸出的數(shù)據(jù)流到目的地。數(shù)據(jù)一進(jìn)入系統(tǒng)，就被若干進(jìn)程加工或改變，用圓角的矩形表示這些過(guò)程。進(jìn)程可以是程序、過(guò)程以及能夠改變或傳送數(shù)據(jù)的任何事件為了后續(xù)處理，數(shù)據(jù)被保留在數(shù)據(jù)存儲(chǔ)器內(nèi)，這可用末端開(kāi)口的矩形符號(hào)表示。數(shù)據(jù)存儲(chǔ)可以是磁盤(pán)文件、磁

50、帶文件、數(shù)據(jù)庫(kù)、一些筆記或者甚至是人的記憶。最后，數(shù)據(jù)源、數(shù)據(jù)目的地、處理過(guò)程和數(shù)據(jù)存儲(chǔ)之間的數(shù)據(jù)流向用箭頭表示。圖2展示了貨單管理系統(tǒng)的初步的數(shù)據(jù)流程圖。從CUSTOMER（顧客）開(kāi)始，由此事務(wù)進(jìn)入系統(tǒng)，在這所辦理的手續(xù)由PROCESSTRANSATION（事務(wù)處理程序）處理。STOCK保存貨單中每項(xiàng)商品的數(shù)據(jù).為了對(duì)新的事務(wù)處理起作用，事務(wù)處理程序要改變數(shù)據(jù)。同時(shí)，MANAGEMENT（經(jīng)營(yíng)部門(mén)）可通過(guò)COMMUNICATE（通信）存取系統(tǒng)，檢查STOCK中的數(shù)據(jù)，如果需要的話(huà)，請(qǐng)求重新訂貨.訂貨單一經(jīng)核準(zhǔn)。GENERATEREORDER（產(chǎn)生訂貨單程序）就向SUPPLIER（供應(yīng)商）發(fā)出

51、需要的數(shù)據(jù)，供應(yīng)商就把貨運(yùn)送到商店。注意，因?yàn)橛嗀洷憩F(xiàn)為某種待定的商品或某些商品在清單中的變化，所以把訂貨作為事務(wù)處理。圖2數(shù)據(jù)流程圖描述了邏輯系統(tǒng)。下一步該追溯該系統(tǒng)的數(shù)據(jù)流向了。從數(shù)據(jù)的目的地SUPPLIEF開(kāi)始。例如，重訂貨單送給了供貨商們，商店可能想要25條工作褲，為了填寫(xiě)訂貨單，供應(yīng)商需要商品的說(shuō)明和再訂貨的數(shù)量，那么，這些數(shù)據(jù)從什么地方來(lái)呢？由于數(shù)據(jù)是Generatereorder輸出的，所以既要有數(shù)據(jù)輸入給它，還要有數(shù)據(jù)經(jīng)過(guò)它的處理而產(chǎn)生。數(shù)據(jù)從STOCK流入Generatereorder,因此商品說(shuō)明和訂貨數(shù)量必定存放在STOCK中。另外一些數(shù)據(jù)，例如購(gòu)買(mǎi)的貨物品種和數(shù)量由CU

52、STOMER產(chǎn)生，還有一些數(shù)據(jù)，例如銷(xiāo)售價(jià)格和訂貨點(diǎn)由MANAGEMENT產(chǎn)生，或者由它提出要求。例如，某種已知貨物的現(xiàn)存量就是由某個(gè)處理過(guò)程中的某種算法產(chǎn)生出來(lái)的。分析員逐步地、有條理地區(qū)分了系統(tǒng)要求輸入、存儲(chǔ)、處理、產(chǎn)生或輸出的應(yīng)該分別是哪些數(shù)據(jù)元素。為了記錄數(shù)據(jù)元素，分析員必須把每個(gè)數(shù)據(jù)列在數(shù)據(jù)字典內(nèi)簡(jiǎn)單的數(shù)據(jù)字典可建立在索引卡片上，但計(jì)算機(jī)化的數(shù)據(jù)字典已經(jīng)變得日益流行了。數(shù)據(jù)字典是描述和定義數(shù)據(jù)的一個(gè)數(shù)據(jù)集合，不僅在整個(gè)系統(tǒng)的分析與設(shè)計(jì)過(guò)程中有用，而且在實(shí)現(xiàn)階段經(jīng)常被用來(lái)建立數(shù)據(jù)庫(kù)。分析階段的目標(biāo)是定義系統(tǒng)的主要功能和有條理地確定數(shù)據(jù)元素。記住，它的目標(biāo)是把用戶(hù)的需求轉(zhuǎn)換成技術(shù)術(shù)語(yǔ)。因?yàn)橄到y(tǒng)是由用戶(hù)提出的，所以首先要確定用戶(hù)的需求。用戶(hù)只是從功能和數(shù)據(jù)出發(fā)考慮系統(tǒng)，他們并不具體設(shè)計(jì)程序、文件和硬件，并且在這個(gè)初始的帶有決定性的分析階段，分析員必須像用戶(hù)而不像程序設(shè)計(jì)員一樣去思考問(wèn)題。這是該階段的基本要求。數(shù)據(jù)