SoftwareEngineering软体工程(英文课件).ppt

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1、1,Software Engineering軟體工程,2,Course Objectives,To learn about all the difficulties in developing software so that we can avoid pitfalls and myths in software designTo learn about different software processes so that we can choose a suitable oneTo learn to design high-quality efficient software so th

2、at it is usable and maintainableTo learn about advanced methods for software engineering,3,Course Contents,Introduction to Software EngineeringSoftware ProcessesRequirements EngineeringSoftware DesignObject-Oriented Software DevelopmentSoftware Testing and VerificationSoftware Project ManagementAdva

3、nced Methods,4,Chapter 1Introduction to Software Engineering,An overview of software engineering,including software crisis,myths,methods,evolution,and status,5,Contents,Software CrisisSoftware MythsWhat is Software EngineeringEvolution of Software EngineeringState-of-art in Software Engineering,6,Th

4、e statistics Chaos Report,Standish Group 1995365 IT executives in US companies in diverse industry segments.8,380 projects,average cost overrun=189%,average time overrun=222%.,61%of originally specified features included,?,In Averages 189%of original budget 221%of original schedule 61%of original fu

5、nctionality,7,Symptom of Software Crisis,About US$250 billions spent per year in the US on application developmentOut of this,about US$140 billions wasted due to the projects getting abandoned or reworked;this in turn because of not following best practices and standards,Ref:Standish Group,1996,8,Sy

6、mptom of Software Crisis,10%of client/server apps are abandoned or restarted from scratch 20%of apps are significantly altered to avoid disaster40%of apps are delivered significantly late,Source:3 year study of 70 large c/s apps 30 European firms.Compuware(12/95),9,Software products:fail to meet use

7、r requirementscrash frequentlyexpensivedifficult to alter,debug,enhanceoften delivered lateuse resources non-optimally,Observed Problems,10,Why is the Statistics so Bad?,Misconception on software developmentSoftware myths,e.g.,the man-month mythFalse assumptionsNot distinguishing the coding of a com

8、puter program from the development of a software productSoftware programs have exponential growth in complexity and difficulty level with respect to size.The ad hoc approach breaks down when size of software increases.,11,Why is the Statistics so Bad?,Software professionals lack engineering training

9、Programmers have skills for programming but without the engineering mindset about a process disciplineInternal complexitiesEssences and accidents made by Fred.Brooks,12,How is Software usually Constructed,The requirements specification was defined like this,The developers understood it in that way,T

10、his is how the problem was solved before.,This is how the problem is solved now,That is the program after debugging,This is how the program is described by marketing dept.,This,in fact,is what the customer wanted;-),13,Software Myths(Customer Perspectives),A general statement of objectives is suffic

11、ient to get started with the development of software.Missing/vague requirements can easily be incorporated/detailed out as they get concretized.Application requirements can never be stable;software can be and has to be made flexible enough to allow changes to be incorporated as they happen.,14,Softw

12、are Myths(Developer Perspectives),Once the software is demonstrated,the job is done.,Usually,the problems just begin!,15,Until the software is coded and is available for testing,there is no way for assessing its quality.,Usually,there are too many tiny bugs inserted at every stage that grow in size

13、and complexity as they progress thru further stages!,Software Myths(Developer Perspectives),16,The only deliverable for a software development project is the tested code.,The code is only the externally visible component of the entire software complement!,Software Myths(Developer Perspectives),17,So

14、ftware Myths(Management Perspectives),As long as there are good standards and clear procedures in my company,I shouldnt be too concerned.,But the proof of the pudding is in the eating;not in the Recipe!,18,Software Myths(Management Perspectives),As long as my software engineers(!)have access to the

15、fastest and the most sophisticated computer environments and state-of-the-art software tools,I shouldnt be too concerned.,The environment is only one of the several factors that determine the quality of the end software product!,19,Software Myths(Management Perspectives),When my schedule slips,what

16、I have to do is to start a fire-fighting operation:add more software specialists,those with higher skills and longer experience-they will bring the schedule back on the rails!,Unfortunately,software business does not entertain schedule compaction beyond a limit!,20,Misplaced Assumptions,All requirem

17、ents can be pre-specifiedUsers are experts at specification of their needsUsers and developers are both good at visualizationThe project team is capable of unambiguous communication,Ref:Larry Vaughn,21,Usually small in sizeAuthor himself is sole userSingle developerLacks proper user interfaceLacks p

18、roper documentationAd hoc development.,LargeLarge number of usersTeam of developersWell-designed interfaceWell documented&user-manual preparedSystematic development,Programs,Software Products,Confused with Programs and Products,22,Software Programming Software Engineering,Software programming:the pr

19、ocess of translating a problem from its physical environment into a language that a computer can understand and obey.(Websters New World Dictionary of Computer Terms)Single developer“Toy”applicationsShort lifespanSingle or few stakeholdersArchitect=Developer=Manager=Tester=Customer=UserOne-of-a-kind

20、 systemsBuilt from scratchMinimal maintenance,23,Software Programming Software Engineering,Software engineeringTeams of developers with multiple rolesComplex systemsIndefinite lifespanNumerous stakeholdersArchitect Developer Manager Tester Customer UserSystem familiesReuse to amortize costsMaintenan

21、ce accounts for over 60%of overall development costs,24,What is Software?,Software is a set of items or objects that form a“configuration”that includes programs documents data.(“Software Engineering-a practitioners approach,”Pressman,5ed.McGraw-Hill),25,What is Software(ctd.)?,Or you may want to say

22、:Software consists of(1)instructions(computer programs)that when executed provided desired function and performance,(2)data structures that enable the programs to adequately manipulate information,and(3)documents that describe the operation and use of the programs.,26,What is Software(ctd.)?,But the

23、se are only the concrete part of software that may be seen,there exists also invisible part which is more important:Software is the dynamic behavior of programs on real computers and auxiliary equipment.“a software product is a model of the real world,and the real world is constantly changing.”Softw

24、are is a digital form of knowledge.(“Software Engineering,”6ed.Sommerville,Addison-Wesley,2000),27,Unique Characteristics of Software,Software is malleableSoftware construction is human-intensiveSoftware is intangible and hard to measureSoftware problems are usually complexSoftware directly depends

25、upon the hardwareIt is at the top of the system engineering“food chain”Software doesnt wear out but will deteriorateSoftware solutions require unusual rigorSoftware has discontinuous operational nature,28,Casting the Term,The field of software engineering was born in NATO Conferences,1968 in respons

26、e to chronic failures of large software projects to meet schedule and budget constraintsSince then,term became popular because software is getting more and more important to industry and business but the“software crisis”still persists.,29,What is Software Engineering?,Different focuses for this term

27、 exist in various textbooks.Some are listed below.The application of a systematic,disciplined,quantifiable approach to development,operation,and maintenance of software;that is,the application of engineering to software.(IEEE Standard Computer Dictionary,610.12,ISBN 1-55937-079-3,1990),30,What is So

28、ftware Engineering?(ctd),Software engineering is concerned with the theories,methods and tools for developing,managing and evolving software products.(I.Sommerville,6ed.)A discipline whose aim is the production of quality software,delivered on time,within budget,and satisfying users needs.(Stephen R

29、.Schach,Software Engineering,2ed.)Multi-person construction of multi-version software(Parnas,1987),31,The practical application of scientific knowledge in the design and construction of computer programs and the associated documentation required to develop,operate and maintain them(B.W.Boehm)The est

30、ablishment and use of sound engineering principles in order to obtain economically software that is reliable and works efficiently on real machines(F.L.Bauer),What is Software Engineering?(ctd.),32,The technological and managerial discipline concerned with systematic production and maintenance of so

31、ftware products that are developed and modified on time and within cost constraints(R.Fairley)A discipline that deals with the building of software systems which are so large that they are built by a team or teams of engineers(Ghezzi,Jazayeri,Mandrioli),What is Software Engineering?(ctd.),33,Other D

32、efinitions of Software Engineering,“A systematic approach to the analysis,design,implementation and maintenance of software.”(The Free On-Line Dictionary of Computing)“The systematic application of tools and techniques in the development of computer-based applications.”(Sue Conger in The New Softwar

33、e Engineering)“Software Engineering is about designing and developing high-quality software.”(Shari Lawrence Pfleeger in Software Engineering-The Production of Quality Software),34,So,Software Engineering is,Scopestudy of software process,development principles,techniques,and notationsGoalsproductio

34、n of quality software,delivered on time,within budget,satisfying customers requirements and users needs,35,Software Process,Waterfall life cyclePrototypingSpiral modelAutomatic synthesis modelObject-oriented model4 GL model,36,Traditional Software Engineering,Software Systems,Data,Function,Behavior,

35、Entity-RelationDiagram,Data FlowDiagram,State TransitionDiagram,37,Object-Oriented Software Engineering,Software Systems,Function,Object,Behavior,Data FlowDiagram,ClassDiagram,State Chart,38,Evolution of Software Industry,Independent Programming ServiceSoftware ProductEnterprise SolutionPackaged Sof

36、tware for the Mass,39,Independent Programming Services(Era 1),Feb 1955,Elmer Kubie and John Sheldon founded CUC the First Software Company that devoted to the construction of software especially for hardware company.Promoting Software Industry:two Major Projects,SABRE,airline reservation system,$30

37、million.SAGE,air defense system(19491962)700/1000 programmers in the US.$8 billion.,40,Software Product(Era 2),1964 Martin Goetz developed Flowchart Software-Autoflow for RCA,but rejected.Sale to the customer of RCA&IBM.Develop and market software products not specifically designed for a particular

38、hardware platform.MARK IV,a pre-runner for the database management system.IBM unbundled software from hardware.,41,Enterprise Solutions(Era 3),Dietmar Hopp.IBM GermanySystems,Applications and Products(SAP)$3.3billion(1997)Setting up shop in Walldorf,Germany.Marked by the emergence of enterprise solu

39、tions providers.e.g.Baan 1978.Netherlands.$680 million(1997)Oracle 1977.U.S.Larry Ellison.ERP,$45 billion(1997),42,Packaged Software for the Masses(Era 4),Software products for the masses.1979.VisiCalc,Spreadsheet program.August 1981:The deal of the century.Bill Gates bought the first version of the

40、 OS from a small firm called Seattle Computer Products for$50,000 without telling them it was for IBM.The development of the IBM PC,1981,initiated a 4th software era.PC-based mass-market software.Few additional services are required for installation.Microsoft reached revenues of$11.6 billion.Package

41、d Software Products,$57 billion(1997),43,Internet Software and Services(Era 5),Internet and value-added services period,1994.Wwith Netscapes browser software for the internet.,44,Object-Oriented,Ad hoc,Data flow-based,Data structure-based,Control flow-based,Evolution of Design Techniques,45,Related

42、Knowledge,46,IT Market,Hardwareproducts,Hardwaremaintenance,Software Products&Services,Processing Servicesand Internet Services,EmbeddedSoftware,ProfessionalService,SoftwareProducts,EnterpriseSolution,PackagedMass-MarketSoftware,47,Software Products and Services,Enterprise SolutionsIBMOracleComputer

43、 AssociatesSAPHPFujitsuHitachiParametric TechnologyPeople SoftSiemens,Packaged Mars-Market SoftwareMicrosoftIBMComputer AssociatesAdobeNovellSymantecIntuitAutodeskAppleThe Learning Company,Professional Software ServicesAnderson ConsultingIBMEDSCSCScience ApplicationsCap GeminiHpDECFujitsuBSO Origin,

44、48,Software Engineering Today?,Organizations“go with what has worked in the past”Everyone is too busy getting product out the door to spend time in education or training or addressing these problems effectively“Out of date”practices become institutionalized,49,Software Engineering Today?,Few people

45、know,or can integrate,best practices Unable to adopt and utilize proven methodologies in timely fashion Although significant improvements have been made in specific areas,the rapidly evolving nature of the software industry has resulted in little overall improvement in the overall situation.,50,Not

46、Crisis,but a Chronic Problem,The crisis persistsAfter 35 years later,the software“crisis”is still with usMajor problems are still the same:poor quality(correctness,usability,maintainability,etc)over budgetdelivered late,or not at allIt is not a crisis but a chronic problem It becomes a persistent,ch

47、ronic condition that software industry has to face with,51,Whats Wrong?,Does software engineering have no progress at all?Not quite true.We have indeed seen a lot of improvements,e.g.high level programming,object-oriented technology,etc.But it does not achieve its promise,why?production of fault-fre

48、e software,delivered on time and within budget,that satisfies the users needs,and is easy to maintain,etc.,52,A More Close Look,The comparison with 1995s report does show that there is some progress in the past eight years.,53,So,Whats the Problem?,Software issues:software industry has changes a lot

49、 in the past yearsEducation issue:more emphasis on methods and tools but lack of sufficient education and training on peopleProcess and quality issue:there lacks of a set of known proven practices for software engineers to follow with,54,Software Changes in the Past Years,Changes in software over ti

50、me:grew in size from 10s or 100s of lines to 1000s to 1,000,000s of lines of codeoperating environment changed from simple“batch”operations to complex multiprogramming systems,to time-sharing and distributed computing to todays Internet network computing environment.,55,Software Changes in the Past