软件工程毕业论文外文文献—软件工程.docx

软件工程毕业论文外文文献—软件工程.docx

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外文原文

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

1、Introduction

Thedevelopmentofcorporatedatabaseswillbeoneofthemostimportantdata-processingactivitiesfortherestofthe1970s.Datewillbeincreasinglyregardedasavitalcorporateresource,whichmustbeorganizedsoastomaximizetheirvalue.Inadditiontothedatabaseswithinanorganization,avastnewdemandisgrowingfordatabaseservices,whichwillcollect,organize,andselldata.

Thefilesofdatawhichcomputerscanusearegrowingatastaggeringrate.Thegrowthrateinthesizeofcomputerstorageisgreaterthanthegrowthinthesizeorpowerofanyothercomponentintheexplodingdataprocessingindustry.Themoredatathecomputershaveaccessto,thegreateristheirpotentialpower.Inallwalksoflifeandinallareasofindustry,databankswillchangetheareasofwhatitispossibleformantodo.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-statestorageoffersthepossibilityofparallelsearchoperationandassociativememory.

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.

Therearemanyinterlockingquestionsinthedesignofdata-basesystemsandmanytypesoftechniquethatonecanuseisanswertothequestionsomany;infact,thatoneoftenseesvaluableapproachesbeingoverlookedinthedesignandvitalquestio