軟件工程(研究生)全冊(cè)配套課件3

軟件工程(研究生)全冊(cè)配套課件3NationalEngineeringCenterforCADSoftwareEngineeringHuazhongUniversityofScienceandTechnologyNationalEngineeringCenterforCADDr.LiuQinghualiuqh@

Chapter1:IntroductionObjectives:tointroducesoftwareengineeringandtoprovideaframeworkforunderstandingsoftwareengineering.Understandwhatsoftwareengineeringisandwhyitisimportant;Understandthatthedevelopmentofdifferenttypesofsoftwaresystemsmayrequiredifferentsoftwareengineeringtechniques;Understandsomeethicalandprofessionalissuesthatareimportantforsoftwareengineers;Beintroducedtothreesystems,ofdifferenttypes,thatwillbeusedasexamplesthroughoutthebook.HistoryofsoftwareengineeringThenotionof‘softwareengineering’wasfirstproposedin1968ataconferenceheldtodiscusswhatwasthencalledthe‘softwarecrisis’.Itbecameclearthatindividualapproachestoprogramdevelopmentdidnotscaleuptolargeandcomplexsoftwaresystems.Thesewereunreliable,costmorethanexpected,andweredeliveredlate.Throughoutthe1970sand1980s,avarietyofnewsoftwareengineeringtechniquesandmethodsweredeveloped,suchasstructuredprogramming,informationhidingandobject-orienteddevelopment.Toolsandstandardnotationsweredevelopedandarenowextensivelyused.ContentsProfessionalSoftwareDevelopmentSoftwareengineeringethicsCaseStudySoftwareandsoftwareengineeringWecan’trunthemodernworldwithoutsoftware.Softwaresystemsareabstractandintangible.Theyarenotconstrainedbythepropertiesofmaterials,governedbyphysicallaws,orbymanufacturingprocesses.Thissimplifiessoftwareengineering.Softwaresystemscanquicklybecomeextremelycomplex,difficulttounderstand,andexpensivetochange.Therearemanydifferenttypesofsoftwaresystems,fromsimpleembeddedsystemstocomplex,worldwideinformationsystems.Itispointlesstolookforuniversalnotations,methods,ortechniquesforsoftwareengineeringbecausedifferenttypesofsoftwarerequiredifferentsoftwareengineeringtechniques.SoftwareFailuresSoftwarefailuresaremainlyconsequenceoftwofactors:Increasingdemands

andChangingdemandsSystemshavetobebuiltanddeliveredmorequicklyLarger,evenmorecomplexsystemsarerequiredSystemshavetohavenewcapabilitiesthatwerepreviouslythoughttobeimpossible.ExistingsoftwareengineeringmethodscannotcopeandnewSEtechniqueshavetobedevelopedtomeetthesenewdemands.LowexpectationsItisrelativelyeasytowritecomputerprogramswithoutusingsoftwareengineeringmethodsandtechniques.Manycompanieshavedriftedintosoftwaredevelopmentastheirproductsandserviceshaveevolved.Theydonotusesoftwareengineeringmethodsintheireverydaywork.1.1ProfessionalsoftwaredevelopmentLotsofpeoplewriteprograms.Professionalsoftware,intendedforusebysomeoneapartfromitsdeveloper,isusuallydevelopedbyteamsratherthanindividualsSoftwareengineeringisintendedtosupportprofessionalsoftwaredevelopmentratherthanindividualprogramming.Somefrequentlyaskedquestions(FAQs)aboutsoftwareengineeringarelistinthefollowingpage.FAQsaboutsoftwareengineeringQuestionAnswerWhatissoftware?Computerprogramsandassociateddocumentation.Softwareproductsmaybedevelopedforaparticularcustomerormaybedevelopedforageneralmarket.Whataretheattributesofgoodsoftware?Goodsoftwareshoulddelivertherequiredfunctionalityandperformancetotheuserandshouldbemaintainable,dependableandusable.Whatissoftwareengineering?Softwareengineeringisanengineeringdisciplinethatisconcernedwithallaspectsofsoftwareproduction.Whatarethefundamentalsoftwareengineeringactivities?Softwarespecification,softwaredevelopment,softwarevalidationandsoftwareevolution.Whatisthedifferencebetweensoftwareengineeringandcomputerscience?Computersciencefocusesontheoryandfundamentals;softwareengineeringisconcernedwiththepracticalitiesofdevelopinganddeliveringusefulsoftware.Whatisthedifferencebetweensoftwareengineeringandsystemengineering?Systemengineeringisconcernedwithallaspectsofcomputer-basedsystemsdevelopmentincludinghardware,softwareandprocessengineering.Softwareengineeringispartofthismoregeneralprocess.Whatarethekeychallengesfacingsoftwareengineering?Copingwithincreasingdiversity,demandsforreduceddeliverytimesanddevelopingtrustworthysoftware.Whatarethecostsofsoftwareengineering?Roughly60%ofsoftwarecostsaredevelopmentcosts,40%aretestingcosts.Forcustomsoftware,evolutioncostsoftenexceeddevelopmentcosts.Whatarethebestsoftwareengineeringtechniquesandmethods?Whileallsoftwareprojectshavetobeprofessionallymanagedanddeveloped,differenttechniquesareappropriatefordifferenttypesofsystem.Forexample,gamesshouldalwaysbedevelopedusingaseriesofprototypeswhereassafetycriticalcontrolsystemsrequireacompleteandanalyzablespecificationtobedeveloped.Youcan’t,therefore,saythatonemethodisbetterthananother.Whatdifferenceshasthewebmadetosoftwareengineering?Thewebhasledtotheavailabilityofsoftwareservicesandthepossibilityofdevelopinghighlydistributedservice-basedsystems.Web-basedsystemsdevelopmenthasledtoimportantadvancesinprogramminglanguagesandsoftwarereuse.TwokindsofsoftwareproductsGenericproductsThesearestand-alonesystemsthatareproducedbyadevelopmentorganizationandsoldontheopenmarkettoanycustomerwhoisabletobuythem.Theorganizationthatdevelopsthesoftwarecontrolsthesoftwarespecification.Customized(orbespoke)productsThesearesystemsthatarecommissionedbyaparticularcustomer.Thespecificationisusuallydevelopedandcontrolledbytheorganizationthatisbuyingthesoftware.AnimportantdifferencebetweenthetwoDistinctionisbecomingblurredMoreandmoresystemsarenowbeingbuiltwithagenericproductasabase,whichisthenadaptedtosuittherequirementsofacustomer.EnterpriseResourcePlanning(ERP)systems,suchastheSAPsystem,arethebestexamplesofthisapproach.Here,alargeandcomplexsystemisadaptedforacompanybyincorporatinginformationaboutbusinessrulesandprocesses,reportsrequired,andsoon.AttributesofgoodsoftwareProductcharacteristicDescriptionMaintainabilitySoftwareshouldbewritteninsuchawaysothatitcanevolvetomeetthechangingneedsofcustomers.Thisisacriticalattributebecausesoftwarechangeisaninevitablerequirementofachangingbusinessenvironment.DependabilityandsecuritySoftwaredependabilityincludesarangeofcharacteristicsincludingreliability,securityandsafety.Dependablesoftwareshouldnotcausephysicaloreconomicdamageintheeventofsystemfailure.Malicioususersshouldnotbeabletoaccessordamagethesystem.EfficiencySoftwareshouldnotmakewastefuluseofsystemresourcessuchasmemoryandprocessorcycles.Efficiencythereforeincludesresponsiveness,processingtime,memoryutilisation,etc.AcceptabilitySoftwaremustbeacceptabletothetypeofusersforwhichitisdesigned.Thismeansthatitmustbeunderstandable,usableandcompatiblewithothersystemsthattheyuse.1.1.1SoftwareengineeringDefinition:anengineeringdisciplinethatisconcernedwithallaspectsofsoftwareproductionfromtheearlystagesofsystemspecificationthroughtomaintainingthesystemafterithasgoneintouse.Twokeyphases:Engineeringdiscipline

Engineersmakethingswork.Theyapplytheories,methods,andtoolswheretheseareappropriate.Engineersalsorecognizethattheymustworktoorganizationalandfinancialconstraints.Allaspectsofsoftwareproduction

Softwareengineeringisnotjustconcernedwiththetechnicalprocessesofsoftwaredevelopment.Italsoincludesactivitiessuchassoftwareprojectmanagementandthedevelopmentoftools,methods,andtheoriestosupportsoftwareproduction.WhysoftwareengineeringisimportantIndividualsandsocietyrelyonadvancedsoftwaresystems.Weneedtobeabletoproducereliableandtrustworthysystemseconomicallyandquickly.Itisusuallycheaper,inthelongrun,tousesoftwareengineeringmethodsandtechniquesforsoftwaresystemsratherthanjustwritetheprogramsasifitwasapersonalprogrammingproject.Formosttypesofsystems,themajorityofcostsarethecostsofchangingthesoftwareafterithasgoneintouse.SoftwareprocessAsoftwareprocessisasequenceofactivitiesthatleadstotheproductionofasoftwareproduct.Fourfundamentalactivitiescommontosoftwareprocesses.Softwarespecification,wherecustomersandengineersdefinethesoftwarethatistobeproducedandtheconstraintsonitsoperationSoftwaredevelopment,wherethesoftwareisdesignedandprogrammed.Softwarevalidation,wherethesoftwareischeckedtoensurethatitiswhatthecustomerrequires.Softwareevolution,wherethesoftwareismodifiedtoreflectchangingcustomerandmarketrequirements.1.1.2SoftwareengineeringdiversityNouniversalsoftwareengineeringmethodsandtechniquesthataresuitableforallsystemsandallcompanies.Themostsignificantfactorindeterminingwhichsoftwareengineeringmethodstobeusedistheapplicationtypethatisbeingdeveloped.Stand-aloneapplications

CADprograms,etc.Interactivetransaction-basedapplicationsEmbeddedcontrolsystems

SoftwareinmobilephoneBatchprocessingsystemsPeriodicbillingsystemsEntertainmentsystemsSystemsformodelingandsimulationDatacollectionsystemsSystemofsystemsSoftwareEngineeringfundamentalsTheyshouldbedevelopedusingamanagedandunderstooddevelopmentprocess.Dependabilityandperformanceareimportantforalltypesofsystems。Understandingandmanagingthesoftwarespecificationandrequirements(whatthesoftwareshoulddo)areimportant.Youshouldmakeaseffectiveuseaspossibleofexistingresources.1.1.3SEandtheWebThedevelopmentoftheWorldWideWebhashadaprofoundeffectonallofourlives.Thesoftwarewasdeployedonawebserver.Thismadeitmuchcheapertochangeandupgradethesoftware.Thenextstageinthedevelopmentofweb-basedsystemswasthenotionofwebservices.Thenotionof‘softwareasaservice’hasbeendeveloped.Ithasbeenproposedthatsoftwarewillrunon‘computingclouds’thatareaccessedovertheInternet.Theadventofthewebhasledtoasignificantchangeinthewaythatbusinesssoftwareisorganized.ChangesofWeb-basedsystemsareengineeredSoftwarereusehasbecomethedominantapproachforconstructingweb-basedsystems.Itisnowgenerallyrecognizedthatitisimpracticaltospecifyalltherequirementsforsuchsystemsinadvance.Userinterfacesareconstrainedbythecapabilitiesofwebbrowsers.Webformswithlocalscriptingaremorecommonlyused.Applicationinterfacesonweb-basedsystemsareoftenpoorer.1.2SoftwareEngineeringethicsSoftwareengineeringiscarriedoutwithinasocialandlegalframework.thereareareaswherestandardsofacceptablebehaviorarenotboundbylawsbutbythemoretenuousnotionofprofessionalresponsibility.Someoftheseare:Confidentiality

Youshouldnormallyrespecttheconfidentialityofyouremployersorclientsirrespectiveofwhetherornotaformalconfidentialityagreementhasbeensigned.Competence

Youshouldnotmisrepresentyourlevelofcompetence.IntellectualpropertyrightsYoushouldbeawareoflocallawsgoverningtheuseofintellectualpropertysuchaspatentsandcopyright.ComputermisuseYoushouldnotuseyourtechnicalskillstomisuseotherpeople’scomputers.1.3CaseStudyExamplesfromthreedifferenttypesofsystemsareusedthroughoutthebook.Anappropriateexampleisusedwhendiscussingconceptssuchassafetyanddependability,systemmodeling,reuse,etc.AnembeddedsystemThisisasystemwherethesoftwarecontrolsahardwaredeviceandisembeddedinthatdevice.AninformationsystemThisisasystemwhoseprimarypurposeistomanageandprovideaccesstoadatabaseofinformation.Asensor-baseddatacollectionsystemThisisasystemwhoseprimarypurposeistocollectdatafromasetofsensorsandprocessthatdatainsomeway.Case1:AninsulinpumpcontrolsystemInsulinpumphardwareAninsulinpumpcontrolsystemActivitymodeloftheinsulinpumpAninsulinpumpcontrolsystemTwoessentialhigh-levelrequirementsthatthissystemmustmeet:Thesystemshallbeavailabletodeliverinsulinwhenrequired.ThesystemshallperformreliablyanddeliverthecorrectamountofinsulintocounteractthecurrentlevelofbloodsugarCase2:ApatientinformationsystemformentalhealthcareTheMHC-PMS(MentalHealthCare-PatientManagementSystem)isaninformationsystemthatisintendedforuseinclinics.Ithastwooverallgoals:Togeneratemanagementinformationthatallowshealthservicemanagerstoassessperformanceagainstlocalandgovernmenttargets.Toprovidemedicalstaffwithtimelyinformationtosupportthetreatmentofpatients.Case2:OrganizationofMHC-PMSCase2:UsersofMHC-PMSUsersofthesystemincludeclinicalstaffsuchasdoctors,nurses,andhealthvisitors.Nonmedicalusersincludereceptionistswhomakeappointments,medicalrecordsstaffwhomaintaintherecordssystem,andadministrativestaffwhogeneratereports.Thesystemisusedtorecordinformationaboutpatients(name,address,age,nextofkin,etc.),consultations(date,doctorseen,subjectiveimpressionsofthepatient,etc.),conditions,andtreatments.Reportsaregeneratedatregularintervalsformedicalstaffandhealthauthoritymanagers.Case2:KeyfeaturesofMHC-PMSIndividualcaremanagementClinicianscancreaterecordsforpatients,edittheinformationinthesystem,viewpatienthistory,etc.PatientmonitoringThesystemregularlymonitorstherecordsofpatientsthatareinvolvedintreatmentandissueswarningsifpossibleproblemsaredetected.AdministrativereportingThesystemgeneratesmonthlymanagementreportsshowingthenumberofpatientstreatedateachclinic,thenumberofpatientswhohaveenteredandleftthecaresystem,numberofpatientssectioned,thedrugsprescribedandtheircosts,etc.Case3:AwildernessweatherstationWeatherstationcollectdatafromasetofinstrumentsthatmeasuretemperatureandpressure,sunshine,rainfall,windspeed,andwinddirection.Wildernessweatherstationsarepartofalargersystem,whichisaweatherinformationsystemthatcollectsdatafromweatherstationsandmakesitavailabletoothersystemsforprocessing.Case3:AwildernessweatherstationTheweatherstationsystemThisisresponsibleforcollectingweatherdata,carryingoutsomeinitialdataprocessing,andtransmittingittothedatamanagementsystem.ThedatamanagementandarchivingsystemThissystemcollectsthedatafromallofthewildernessweatherstations,carriesoutdataprocessingandanalysis,andarchivesthedatainaformthatcanberetrievedbyothersystems.ThestationmaintenancesystemThissystemcancommunicatebysatellitewithallwildernessweatherstationstomonitorthehealthofthesesystemsandprovidereportsofproblems.Itcanupdatetheembeddedsoftwareinthesesystems.Intheeventofsystemproblems,thissystemcanalsobeusedtoremotelycontrolawildernessweathersystem.Case3:AwildernessweatherstationEachweatherstationisbattery-poweredandmustbeentirelyself-contained—therearenoexternalpowerornetworkcablesavailable.Allcommunicationsarethrougharelativelyslow-speedsatellitelinkandtheweatherstationmustincludesomemechanism(solarorwindpower)tochargeitsbatteries.Thestationsoftwareisthereforenotjustconcernedwithdatacollection.Itmustalso:Monitortheinstruments,power,andcommunicationhardwareandreportfaultstothemanagementsystem.Managethesystempower,ensuringthatbatteriesarechargedwhenevertheenvironmentalconditionspermitbutalsothatgeneratorsareshutdowninpotentiallydamagingweatherconditions,suchashighwind.Allowfordynamicreconfigurationwherepartsofthesoftwarearereplacedwithnewversionsandwherebackupinstrumentsareswitchedintothesystemintheeventofsystemfailure.KeypointsofChapter1Softwareengineeringisanengineeringdisciplinethatisconcernedwithallaspectsofsoftwareproduction.Softwareisnotjustaprogramorprogramsbutalsoincludesdocumentation.Essentialsoftwareproductattributesaremaintainability,dependability,security,efficiency,andacceptability.Thesoftwareprocessincludesalloftheactivitiesinvolvedinsoftwaredevelopment.Thehighlevelactivitiesofspecification,development,validation,andevolutionarepartofallsoftwareprocesses.Thefundamentalnotionsofsoftwareengineeringareuniversallyapplicabletoalltypesofsystemdevelopment.Thesefundamentalsincludesoftwareprocesses,dependability,security,requirements,andreuse.KeypointsofChapter1Therearemanydifferenttypesofsystemsandeachrequiresappropriatesoftwareengineeringtoolsandtechniquesfortheirdevelopment.Therearefew,ifany,specificdesignandimplementationtechniquesthatareapplicabletoallkindsofsystems.Thefundamentalideasofsoftwareengineeringareapplicabletoalltypesofsoftwaresystems.Thesefundamentalsincludemanagedsoftwareprocesses,softwaredependabilityandsecurity,requirementsengineering,andsoftwarereuse.Softwareengineershaveresponsibilitiestotheengineeringprofessionandsociety.Theyshouldnotsimplybeconcernedwithtechnicalissues.Professionalsocietiespublishcodesofconductthatsetoutthestandardsofbehaviorexpectedoftheirmembers.Exercise1.1.Explainwhyprofessionalsoftwareisnotjusttheprogramsthataredevelopedforacustomer.1.2.Whatisthemostimportantdifferencebetweengenericsoftwareproductdevelopmentandcustomsoftwaredevelopment?Whatmightthismeaninpracticeforusersofgenericsoftwareproducts?1.3.Whatarethefourimportantattributesthatallprofessionalsoftwareshouldhave?Suggestfourotherattributesthatmaysometimesbesignificant.1.4.Apartfromthechallengesofheterogeneity,businessandsocialchange,andtrustandsecurity,identifyotherproblemsandchallengesthatsoftwareengineeringislikelytofaceinthe21stcentury(Hint:thinkabouttheenvironment).1.5.Basedonyourownknowledgeofsomeoftheapplicationtypesdiscussedinsection1.1.2,explain,withexamples,whydifferentapplicationtypesrequirespecializedsoftwareengineeringtechniquestosupporttheirdesignanddevelopment.Exercise1.6.Explainwhytherearefundamentalideasofsoftwareengineeringthatapplytoalltypesofsoftwaresystems.1.7.ExplainhowtheuniversaluseoftheWebhaschangedsoftwaresystems.1.8.Discusswhetherprofessionalengineersshouldbecertifiedinthesamewayasdoctorsorlawyers.1.9.ForeachoftheclausesintheACM/IEEECodeofEthicsshowninFigure1.3,suggestanappropriateexamplethatillustratesthatclause.1.10.Tohelpcounterterrorism,manycountriesareplanningorhavedevelopedcomputersystemsthattracklargenumbersoftheircitizensandtheiractions.Clearlythishasprivacyimplications.Discusstheethicsofworkingonthedevelopmentofthistypeofsystem.NationalEngineeringCenterforCADChapter2

SoftwareProcessHuazhongUniversityofScienceandTechnologyNationalEngineeringCenterforCADLiuQinghualiuqh@Chapter2:SoftwareprocessObjectives:Introduceyoutotheideaofasoftwareprocess—acoherentsetofactivitiesforsoftwareproduction.Understandtheconceptsofsoftwareprocessesandsoftwareprocessmodels;Beintroducedtothreegenericsoftwareprocessmodelsandwhentheymightbeused;Knowaboutthefundamentalprocessactivitiesofsoftwarerequirementsengineering,softwaredevelopment,testing,andevolution;Understandwhyprocessesshouldbeorganizedtocopewithchangesinthesoftwarerequirementsanddesign;UnderstandhowtheRationalUnifiedProcessintegratesgoodsoftwareengineeringpracticetocreateadaptablesoftwareprocesses.Contents2.1Softwareprocessmodels2.2Processactivities2.3Copingwithchange2.4TheRationalUnifiedProcessFouractivitiesofsoftwareprocessmodelTherearemanydifferentsoftwareprocessesbutallmustincludefouractivitiesthatarefundamentaltosoftwareengineering:1.Softwarespecification

Thefunctionalityofthesoftwareandconstraintsonitsoperationmustbedefined.2.SoftwaredesignandimplementationThesoftwaretomeetthespecificationmustbeproduced.3.SoftwarevalidationThesoftwaremustbevalidatedtoensurethatitdoeswhatthecustomerwants.4.SoftwareevolutionThesoftwaremustevolvetomeetchangingcustomerneeds.SoftwareprocessmodelsAsoftwareprocessmodelisasimplifiedrepresentationofasoftwareprocess.Eachprocessmodelrepresentsaprocessfromaparticularperspective,andthusprovidesonlypartialinformationaboutthatprocess.Inthissection,anumberofverygeneralprocessmodelsisintroduced(sometimescalled‘processparadigms’)andarepresentedfromanarchitecturalperspective.Thatis,weseetheframeworkoftheprocessbutnotthedetailsofspecificactivities.ThewaterfallmodelThewaterfallmodelThewaterfallmodelisanexampleofaplan-drivenprocess—inprinciple,youmustplanandschedulealloftheprocessactivitiesbeforestartingworkonthem.Inprinciple,thewaterfallmodelshouldonlybeusedwhentherequirementsarewellunderstoodandunlikelytochangeradicallyduringsystemdevelopment.Animportantvariantofthewaterfallmodelisformalsystemdevelopment.Formaldevelopmentprocesses,suchasthatbasedontheBmethodareparticularlysuitedtothedevelopmentofsystemsthathavestringentsafety,reliability,orsecurityrequirements.CleanroomsoftwareengineeringOriginallydevelopedbyIBMIntheCleanroomprocesseachsoftwareincrementisformallyspecifiedandthisspecificationistransformedintoanimplementation.Softwarecorrectnessisdemonstratedusingaformalapproach.Thereisnounittestingfordefectsintheprocessandthesystemtestingisfocusedonassessingthesystem’sreliability.TheobjectiveoftheCleanroomprocessiszero-defectssoftwaresothatdeliveredsystemshaveahighlevelofreliability.IncrementaldevelopmentThesystemisdevelopedasaseriesofversions(increments),witheachversionaddingfunctionalitytothepreviousversion.IncrementaldevelopmentIncrementaldevelopmentisbasedontheideaofdevelopinganinitialimplementation,exposingthistousercommentandevolvingitthroughseveralversionsuntilanadequatesystemhasbeendeveloped.Specification,development,andvalidationactivitiesareinterleavedratherthanseparate,withrapidfeedbackacrossactivities.Incrementalsoftwaredevelopment,whichisafundamentalpartofagileapproaches,isbetterthanawaterfallapproachformostbusiness,e-commerce,andpersonalsystems.Incrementaldevelopment:benefitsIncrementaldevelopmenthasthreeimportantbenefits,comparedtothewaterfallmodel:1.Thecostofaccommodatingchangingcustomerrequirementsisreduced.Theamountofanalysisanddocumentationthathastoberedoneismuchlessthanisrequiredwiththewaterfallmodel.2.Itiseasiertogetcustomerfeedbackonthedevelopmentworkthathasbeendone.Customerscancommentondemonstrationsofthesoftwareandseehowmuchhasbeenimplemented.3.Morerapiddeliveryanddeploymentofusefulsoftwaretothecustomerispossible,evenifallofthefunctionalityhasnotbeenincluded.

CustomersareabletouseandgainvaluefromthesoftwareearlierthanispossiblewithawaterfallprocessProblemswithIncrementaldevelopmentFromamanagementperspective,theincrementalapproachhastwoproblems:Theprocessisnotvisible.Managersneedregulardeliverablestomeasureprogress.Ifsystemsaredevelopedquickly,itisnotcost-effectivetoproducedocumentsthatreflecteveryversionofthesystem.Systemstructuretendstodegradeasnewincrementsareadded.Unlesstimeandmoneyisspentonrefactoringtoimprovethesoftware,regularchangetendstocorruptitsstructure.Incorporatingfurthersoftwarechangesbecomesincreasinglydifficultandcostly.Reuse-orientedsoftwareengineeringThesystemdevelopmentprocessfocusesonintegratingexistedcomponentsintoasystemratherthandevelopingthemfromscratch.Theintermediatestagesinareuse-orientedprocessaredifferent.Thesestagesare:1Componentanalysis

Giventherequirementsspecification,asearchismadeforcomponentstoimplementthatspecification.2RequirementsmodificationTherequirementsareanalyzedusinginformationaboutthecomponentsthathavebeendiscovered.3SystemdesignwithreuseTheframeworkofthesystemisdesignedoranexistingframeworkisreused.4DevelopmentandintegrationSoftwarethatcannotbeexternallyprocuredisdeveloped,andthecomponentsandCOTS(Commercialof-the-shelfsystems)areintegratedtocreatethenewsystem.Reuse-orientedsoftwareengineeringTherearethreetypesofsoftwarecomponentthatmaybeusedinareuse-orientedprocess:1.Webservicesthataredevelopedaccordingtoservicestandardsandwhichareavailableforremoteinvocation.2.Collectionsofobjectsthataredevelopedasapackagetobeintegratedwithacomponentframeworksuchas.NETorJ2EE.3.Stand-alonesoftwaresystemsthatareconfiguredforuseinaparticularenvironment.SoftwarecomponentsReuse-orientedsoftwareengineeringhastheobviousadvantageofreducingtheamountofsoftwaretobedevelopedandsoreducingcostandrisks.Itusuallyalsoleadstofasterdeliveryofthesoftware.Requirementscompromisesareinevitableandthismayleadtoasystemthatdoesnotmeettherealneedsofusers.Somecontroloverthesystemevolutionislostasnewversionsofthereusablecomponentsarenotunderthecontroloftheorganizationusingthem.Prosandco