外文文献翻译软件工程计算机.docx
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外文文献翻译软件工程计算机.docx
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外文文献翻译软件工程计算机
毕业设计(论文)
外文文献翻译
专业
软件工程
学生姓名
张伯虎
班级
软件121
学号
1210701128
指导教师
徐秀芳
专业系主任
徐秀芳
信息工程学院
Informationsystemdevelopmentanddatabasedevelopment
1.SoftwareEngineering
Softwareisthesequencesofinstructionsinoneormoreprogramminglanguagesthatcompriseacomputerapplicationtoautomatesomebusinessfunction.Engineeringistheuseoftoolsandtechniquesinproblemsolving.Puttingthetwowordstogether,softwareengineeringisthesystemticapplicationoftoolsandtechniquesinthedevelopmentofcomputer-basedapplications.
Thesoftwareengineeringprocessdescribesthestepsittakestodeelopthesystem.Webeginadevelopmentprojectwiththenotionthatthereisaproblemtobesolvedviaautomation.Theprocessishowyougetfromproblemrecognitiontoaworkingsolution.Aqualityprocessisdesirablebecauseitismorelikelytoleadtoaqualityproduct.Theprocessfollowedbyaprojectteamduringthedevelopmentlifecycleofanapplicationshouldbeorderly,goal-oriented,enjoyable,andalearningexperience.
Object-orientedmethodologyisanapproachtosystemlifecycledevelopmentthattakesatop-downviewofdataobjects,theirallowableactions,andtheunderlyingcommunicationrequirementtodefineasystemarchitecture.Thedataandactioncomponentsareencapsulated,thatis,theyarecombinedtogether,toformabstractdatatypesEncapsulationmeansthatifIknowwhatdataIwant,Ialsoknowtheallowableprocessesagainstthatdata.Dataaredesignedaslatticehierarchiesofrelationshipstoensurethattop-down,hierarchicinheritanceandsidewaysrelationshipsareaccommodated.Encapsulatedobjectsareconstrainedonlytocommunicateviamessages.Ataminimum,messagesindicatethereceiverandactionrequested.Messagesmaybemoreelaborate,includingthesenderanddatatobeactedupon.
Thatwetrytoapplyengineeringdisciplinetosoftwaredevelopmentdoesnotmeanthatwehavealltheanswersabouthowtobuildapplications.Onthecontrary,westillbuildsystemsthatarenotusefulandthusarenotused.Partofthereasonforcontinuingproblemsinapplicationdevelopment,isthatweareconstantlytryingtohitamovingtarget.Boththetechnologyandthetypeofapplicationsneededbybusinessesareconstantlychangingandbecomingmorecomplex.Ourabilitytodevelopanddisseminateknowledgeabouthowtosuccessfullybuildsystemsfornewtechnologiesandnewapplicationtypesseriouslylagsbehindtechnologicalandbusinesschanges.
Anotherreasonforcontinuingproblemsinapplicationdevelopmentisthatwearen’talwaysfreetodowhatwelikeanditishardtochangehabitsandculturesfromtheoldwayofdoingthings,aswellasgetuserstoagreewithanewsequenceofeventsoranunfamiliarformatfordocumentation.
Youmightaskthen,ifmanyorganizationsdon’tusegoodsoftwareengineeringpractices,whyshouldIbotherlearningthem?
Therearetwogoodanswerstothisquestion.First,ifyouneverknowtherightthingtodo,youhavenochanceofeverusingit.Second,organizationswillfrequentlyacceptevolutionary,smallstepsofchangeinsteadofrevolutionary,massivechange.Youcanlearnindividualtechniquesthatcanbeappliedwithoutcompletedevotiontoonewayofdevelopingsystems.Inthisway,softwareengineeringcanspeedchangeeintheirorganizationsbydemonstratinghowthetoolsandtechniquesenhancethqualityofboththeproductandtheprocessofbuildingasystem.
2.DataBaseSystem
Thedevelopmentofcorporatedatabaseswillbeoneofthemostimportantdata-processingactivitiesfortherestofthe1970s.Datewillbeincreasinglyregardedasavitalcorporateresource,whichmustbeorganizedsoastomaximizetheirvalue.Inadditiontothedatabaseswithinanorganization,avastnewdemandisgrowingfordatabaseservices,whichwillcollect,organize,andselldata.
Thefilesofdatawhichcomputerscanusearegrowingatastaggeringrate.Thegrowthrateinthesizeofcomputerstorageisgreaterthanthegrowthinthesizeorpowerofanyothercomponentintheexplodingdataprocessingindustry.Themoredatathecomputershaveaccessto,thegreateristheirpotentialpower.Inallwalksoflifeandinallareasofindustry,databankswillchangetheareasofwhatitispossible
Intheendofthiscentury,historianswilllookbacktothecomingofcomputerdatabanksandtheirassociatedfacilitiesasastepwhichchangedthenatureoftheevolutionofsociety,perhapseventuallyhavingagreatereffectonthehumanconditionthaneventheinventionoftheprintingpress.
Somemostimpressivecorporategrowthstoriesofthegenerationarelargelyattributabletotheexplosivegrowthintheneedofinformation.
Thevastmajorityofthisinformationisnotyetcomputerized.However,thecostofdatastoragehardwareisdroppingmorerapidlythanothercostsindataprocessing.Itwillbecomecheapertostoredataoncomputerfilesthantostorethemonpaper.Notonlyprintedinformationwillbestored.Thecomputerindustryisimprovingitscapabilitytostorelinedrawing,datainfacsimileform,photo-graphs,humanspeech,etc.Infact,anyformofinformationotherthanthemostintimatecommunicationsbetweenhumanscanbetransmittedandstoreddigitally.
Therearetwomaintechnologydevelopmentslikelytobecomeavailableinthenearfuture.First,thereareelectromagneticdevicesthatwillholdmuchmoredatathandisksbuthavemuchlongeraccesstime.Second,therearesolid-statetechnologiesthatwillgivemicrosecondaccesstimebutcapacitiesaresmallerthandisks.
Disksthemselvesmaybeincreasedincapacitysomewhat.Forthelongertermfuturethereareanumberofnewtechnologieswhicharecurrentlyworkinginresearchlabswhichmayreplacedisksandmayprovideverylargemicrosecond-access-timedevices.Asteadystreamofnewstoragedevicesisthuslikelytoreachthemarketplaceoverthenext5years,rapidlyloweringthecostofstoringdata.
Giventheavailabletechnologies,itislikelythaton-linedatabaseswillusetwoorthreelevelsofstorage.Onesolid-statewithmicrosecondaccesstime,oneelectromagneticwithaccesstimeofafractionofasecond.Iftwo,three,orfourlevelsofstorageareused,physicalstorageorganizationwillbecomemorecomplex,probablywithpagingmechanismstomovedatabetweenthelevels;solid-statestorageoffersthepossibilityofparallelsearchoperationandassociative
3.memory
Boththequantityofdatastoredandthecomplexityoftheirorganizationaregoingupbyleapsandbounds.Thefirsttrillionbiton-linestoresarenowinuse.inafewyear’stime,storesofthissizemaybecommon.
Aparticularlyimportantconsiderationindatabasedesignistostorethedatasothatthecanbeusedforawidevarietyofapplicationsandsothatthewaytheycanbechangedquicklyandeasily.Oncomputerinstallationpriortothedatabaseeraithasbeenremarkablydifficulttochangethewaydataareused.Differentprogrammersviewthedataindifferentwaysandconstantlywanttomodifythemasnewneedsarisemodification,however,cansetoffachainreactionofchangestoexistingprogramsandhencecanbeexceedinglyexpensivetoaccomplish.
Consequently,dataprocessinghastendedtobecomefrozenintoitsolddatastructures.
Toachieveflexibilityofdatausagethatisessentialinmostcommercialsituations.Twoaspectsofdatabasedesignareimportant.First,itshouldbepossibletointerrogateandsearchthedatabasewithoutthelengthyoperationofwritingprogramsinconventionalprogramminglanguages.Second,thedatashouldbeindependentoftheprogramswhichusethemsothattheycanbeaddedtoorrestructuredwithouttheprogramsbeingchanged.
Theworkofdesigningadatabaseisbecomingincreasingdifficult,especiallyifitistoperforminanoptimalfashion.Therearemanydifferentwaysinwhichdatacanbestructured,andtheyhavedifferenttypesofdataneedtobeorganizedindifferentways.Differentdatahavedifferentcharacteristics,whichoughttoeffectthedataorganization,anddifferentusershavefundamentallydifferentrequirements.Soweneedakindofdatabasemanagementsystem(DBMS)tomanagedata.
Databasedesignusingtheentity-relationshipmodelbeginswithalistoftheentitytypesinvolvedandtherelationshipsamongthem.Thephilosophyofassumingthatthedesignerknowswhattheentitytypesareattheoutsetissignificantlydifferentfromthephilosophybehindthenormalization-basedapproach.
Theentity-relationship(E-R)approachusesentity-relationshipdiagrams.TheE-RapproachrequiresseveralstepstoprodureastructurethatisacceptablebytheparticularDBMS.Thesestepsare:
(1)Dataanalysis
(2)Producingandoptimizingtheentitymodel.
(3)Logicalschemadevelopment
(4)Physicaldatabasedesignprocess.
Developingadatabasestructurefromuserrequirementsiscalleddatabasesdesign.Mostpractitionersagreethattherearetwoseparatephasestothedatabasedesignprocess.Thedesignofalogicaldatabasestructurethatisprocessablebythedatabasemanagementsystem(DBMS)describestheuser’sviewofdata,andistheselectionofaphysicalstructuresuchastheindexedsequentialordirectaccessmethodoftheintendedDBMS.
Currentdatabasedesigntechnologyshowsmanyresidualeffectsofitsoutgrowthfromsingle-recordfiledesignmethods.Filedesignisprimarilyapplicationprogramdependentsincethedatahasbeendefinedandstructuredintermsofindividualapplicationstousethem.TheadventofDBMSrevisedtheemphasisindataandprogramdesignapproaches.
4.DataDescriptionLanguages
Itisnecessaryforboththeprogrammersandthedataadministrator
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