SoftwareEngineering第8版《软件工程》课后习题答案.pdf

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1、1Software Engineering8th editionSolutions to selected exercisesThese solutions are made available far instructional purposes only.They may only be distributed tostudents and it is a condition of distribuiion that they are only distributed by accredited instructorsusing Software Engineering,8th editi

2、on as a textbook.The solutions may be made available tostudents on a password-protected intranet but must not be made available on a publicly-accessibleWWW server.NOT FOR PUBLIC DISTRIBUTION2Solutions to the exercises are organised by chapter and I have provided solutions for 6 or 7 exercisesfor eac

3、h chapter in the book.In some cases,where the material is likely to be unfamiliar or where Ihave found students to have particular difficulties,a larger number of solutions are given.Overall,Ihave provided solutions for about 60%of the exercises.For exercises concerned with ethical issues,there are

4、of course,no definitive solutions.For these exercises,I have included issues that might beaddressed.However,the solutions here are simply indications of what might be expected from studentsattempting the exercises.Many of the exercises have been deliberately designed so that they may beadapted to lo

5、cal situations;therefore they are not specified in a rigid way.Instructors,therefore,mayuse these solutions as a guide but many other possible,equally valid,solutions may also begenerated.There are still a small number of chapters where there are fewer than 6 solutions to exercises.Theseadditional s

6、olutions will be available in the next release of this document in October 2006.NOT FOR PUBLIC DISTRIBUTION Ian Sommerville 20063Chapter 1 IntroductionSolutions provided for Exercises 1.2,1.3,1.4,1.6,1.7 and 1.8.1.2 The essential difference is that in generic software product development,the specifi

7、cation isowned by the product developer.For custom product development,the specification is ownedby the customer.Of course,there may be differences in development processes but this is notnecessarily the case.1.3 For important attributes are maintainability,dependability,performance and usability.Ot

8、herattributes that may be significant could be reusability(can it be reused in other applications),distributability(can it be distributed over a network of processors),portability(can it operateon multiple platforms)and inter-operability(can it work with a wide range of other softwaresystems).Decomp

9、ositions of the 4 key attributes e.g.dependability decomposes to security,safety,availability,etc.are also possible answers.1.4 A software process is what actually goes on when software is developed.A software processmodel is an abstraction and simplification of a process.Process models can be used

10、to helpunderstand real processes and to identify which aspects of these processes could be supportedby CASE tools.1.6 Method support provided by CASE tools:Editors for specific graphical notations usedChecking of the rules1 and guidelines of the methodAdvice to tool users on what to do nextMaintenan

11、ce of a data dictionary-all names used in the systemAutomatic generation of skeleton code from the system modelsGeneration of reports on the design1.7 Problems and challenges for software engineeringDeveloping systems for multicultural useDeveloping systems that can be adapted quickly to new busines

12、s needsDesigning systems for outsourced developmentDeveloping systems that are resistant to attackDeveloping systems that can be adapted and configured by end-usersFinding ways of testing,validating and maintaining end-user developed systemsThere are obviously lots of other problems that could be me

13、ntioned here.1.9 Advantages of certification Certification is a signal to employers of some minimum level of competence.Certification improves the public image of the profession.Certification generally means establishing and checking educational standards and is thereforea mechanism for ensuring cou

14、rse quality.Certification implies responsibility in the event of disputes.Certifying body is likely to be accepted at a national and international level as speaking fbrthe profession,Certification may increase the status of software engineers and attract particularly able peopleinto the profession.D

15、isadvantages of certificationNOT FOR PUBLIC DISTRIBUTION4 Certification tends to lead to protectionism where certified members tend not to protect othersfrom criticism.Certification does not guarantee competence merely that a minimum standard was reached atthe time of certification.,Certification is

16、 expensive and will increase costs to individuals and organisations.Certification tends to stultify change.This is a particular problem in an area where technologydevelopments are very rapid.These are possible discussion points-any discussion on this will tend to be wide ranging and touchon other is

17、sues such as the nature of professionalism,etc.NOT FOR PUBLIC DISTRIBUTION Ian Sommerville 20065Chapter 2 Computer-based system engineeringSolutions provided far Exercises 2.1,2,2,2.3,2.4,2.6,2.7,and 2.8.2.1 Other systems in the systems environment can have unanticipated effects because they haverel

18、ationships with the system over and above whatever formal relationships(e.g.dataexchange)are defined in the system specification.For example,the system may share anelectrical power supply and air conditioning unit,they may be located in the same room(so ifthere is a fire in one system then the other

19、 will be affected)etc.2.2 This is an inherently wicked problem because of the uncertainties associated with theproblem.It is impossible to anticipate exactly when and where a disaster will occur,thenumbers of people involved,the effects on the environment,the technology available to theemergency ser

20、vices,etc.Planning can only be in very general terms and detailed softwarespecifications to cope with specific situations are almost impossible to write.2.3 When a car is decommissioned,not all of its parts are worn out.Software systems can beinstalled in the car to monitor the different parts and t

21、o compute the lifetime which they arelikely to have left.When the car is to be decommissioned,the parts which can potentially bereused can then easily be discovered.2.4 An overall architectural description should be produced to identify sub-systems making up thesystem.Once these have been identified

22、,they may be specified in parallel with other systemsand the interfaces between sub-systems defined.2.6 The key features of the solution are:Database with different types of data Video control system Operator console system River data collection Weather system links Communication control systemSee F

23、igure 2.1.2.7 Possible issues covered in the solution might be:Museums are conservative places and some staff may resent the introduction of newtechnology.Existing museum staff may be asked to deal with problems of the equipment not workingand may not wish to appear unable to deal with this.Other ar

24、eas of the museum may oppose the system because they see it as divertingresources from their work.Different museums may have different preferred suppliers for the equipment so that allequipment used is not identical thus causing support problems.The new displays take up a lot of space and this displ

25、aces other displays.The maintainersof these displays may oppose the introduction of the system.Some museums may have no mechanism for providing technical support for the system.NOT FOR PUBLIC DISTRIBUTION6Met office.Weather infosystemSensor datacollectionOther servicesVidtocuincayiCommscontrollerCam

26、era controlsystemTFigure 2.1 Block diagram of the flood control system2.8 Legacy systems may be critical for the successful operation of a business for two basic reasons They may be an intrinsic part of one or more processes which are fundamental to theoperation of a business.For example,a universit

27、y has a student admissions process andsystems which support this are critical.They must be maintained.,They may incorporate organisational and business knowledge which is simply notdocumented elsewhere.For example,exceptions on student admissions may simply have beencoded directly into the system wi

28、th no paper record of these.Without this system,theorganisation loses valuable knowledge.NOT FOR PUBLIC DISTRIBUTION Ian Sommerville 20067Chapter 3 Critical systemsSolutions provided for Exercises 3.2,3.5,3.6,3.7,3.8,3.10 and 3.11.3.2 Six reasons why dependability is important are:a)Users may not us

29、e the system if they dont trust it.b)System failure may lead to a loss of business.c)An undependable system may lose or damage valuable data.d)An undependable system may damage its external environment.d)The reputation of the company who produced the system may be damaged hence affectingother system

30、s.e)The system may be in breach of laws on consumer protection and the fitness of goods forpurpose.3.5 Internet server:Availability as failure of availability affects a large number of people,reputation of the supplier and hence its current and future income.A computer-control 1 ed scalpel:Safety as

31、 safety-related failures can cause harm to the patient.A directional control system:Reliability as mission failure could result from failure of thesystem to perforin to specification.An personal finance management system:Security because of potential losses to users.3.6 Possible domestic appliances

32、that may include safety-critical software include:Microwave ovenPower tools such as a drill or electric sawLawnmowerCentral heating furnaceGarbage disposal unitFood processor or blender3.7 Ensuring system reliability does not necessarily lead to system safety as reliability isconcerned with meeting

33、the system specification(the system shall)whereas safety isconcerned with excluding the possibility of dangerous behavior(the system shall not).If thespecification does not explicitly exclude dangerous behavior then a system can be reliable butunsafe.3.8 Possible hazard is delivery of too much radia

34、tion to a patient.This can arise because of asystem failure where a dose greater than the specified dose is delivered or an operator failurewhere the dose to be delivered is wrongly input.Possible software features to guard against system failure are the delivery of radiation inincrements with a ope

35、rator display showing the dose delivered and the requirement that theoperator confirm the delivery of the next increment.To reduce the probability of operatorerror,there could be a feature that requires confirmation of the dose to be delivered and thatcompares this to previous doses delivered to tha

36、t patient.Alternatively,two differentoperators could be required to independently input the dose before the machine could operate.3.10 An attack is an exploitation of a system vulnerability.A threat is a circumstance that hasthe potential to cause loss or harm.An attack can lead to a threat if the e

37、xploitation of thevulnerability leads to a threat.However,some attacks can be successful but do not lead tothreats as other system features protect the system.NOT FOR PUBLIC DISTRIBUTION83.11 The ethics of delivery of a faulty system are complex.We know that this happens all the time,especially with

38、 software.Issues that might be discussed include the probability of the faultoccurring and the consequences of the fault-if the fault has potentially seriousconsequences then the decision may be different than if it is a minor,easily recoverable fault.Other issues are the price charged for the syste

39、m(if its low,then what level of quality is itreasonable for the customer to expect).The recovery mechanisms built into the system and thecompensation mechanisms that are in place if consequential damage occurs.Making thecustomer aware of the fault is the honest decision to make but may be unwise fro

40、m a businessperspective.Claims about the reliability of the software should not be made in such circumstances as thesoftware provider does not know how the software will be used and so cannot estimate theprobability of occurrence of the fault.NOT FOR PUBLIC DISTRIBUTION Ian Sommerville 20069Chapter

41、4 Software processesSolutions provided for Exercises 4.1,4.3,47,4.9,4.10 and 4.12.4.1(a)Anti-lock braking system Safety-critical system so method based on formaltransformations with proofs of equivalence between each stage.(b)Virtual reality system System whose requirements cannot be predicted in ad

42、vance soexploratory programming model is appropriate.(c)University accounting system System whose requirements should be stable because ofexisting system therefore waterfall model is appropriate.(d)Interactive timetable System with a complex user interface but which must be stable andreliable.Should

43、 be based on throw-away prototyping to find requirements then eitherincremental development or waterfall model.4.3 The waterfall model is accommodated where there is a low specification risk and no need fbrprototyping etc.fbr risk resolution.The activities in the 2nd quadrant of the spiral model are

44、skipped.The prototyping model is accommodated when the specification phase is limited andthe prototyping(risk resolution)phase predominates.The activities in the 3rd quadrant of thespiral model are skipped or reduced in scope.4.4 Solution to be added.4.7 Components of a design method are:A defined s

45、et of system modelsRules that apply to these modelsGuidelines for design*good practiceA model of the design processFormats for reports on the design4.9 Systems must change because as they are installed in an environment the environment adaptsto them and this adaptation naturally generates new/differ

46、ent system requirements.Furthermore,the systems environment is dynamic and constantly generates new requirementsas a consequence of changes to the business,business goals and business policies.Unless thesystem is adapted to reflect these requirements,its facilities will become out-of-step with thefa

47、cilities needed to support the business and,hence,it will become less useful.4.10 A classification scheme can be helpful for system procurement because it helps identify gapsin the CASE tool coverage in an organisation.Procurement may be aimed at filling thesegaps.Alternatively,a classification sche

48、me may be used to find tools which support a rangeof activities-these may represent the most cost effective purchases if funds are limited.4.12 There are obviously different views here and a lot depends on the development of CASEtechnology in the future.A major difference between the introduction of

49、 CASE technologyand,for example,the introduction of CAD technology which made draftsmen redundant,isthat the routine elements in the design and development of software are relatively minor partsof the whole development process.Therefore,savings are not that large.However,if AItechnology develops so

50、that truly intelligent tools can be developed than,obviously,thissituation will change.NOT FOR PUBLIC DISTRIBUTION10Chapter 5 Project managementSolutions provided for Exercises 5.2,5.3,5.6,5.9,5.10 and 5.11.5.2 Management activities such as proposal writing,project planning and personnel selectionre