软件工程实践者的研究方法chapter11.ppt

These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,1,Chapter 11,Quality Concepts,Slide Set to accompanySoftware Engineering:A Practitioners Approach,7/e by Roger S.PressmanSlides copyright 1996,2001,2005,2009 by Roger S.PressmanFor non-profit educational use onlyMay be reproduced ONLY for student use at the university level when used in conjunction with Software Engineering:A Practitioners Approach,7/e.Any other reproduction or use is prohibited without the express written permission of the author.All copyright information MUST appear if these slides are posted on a website for student use.,酷剃视棋娥历巩寡半谭瞎法辑虐烘哉崭省姬卢噪铰碗镜货蛛宜荧蜜乱啄氯软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,2,Software Quality,In 2005,ComputerWorld Hil05 lamented that“bad software plagues nearly every organization that uses computers,causing lost work hours during computer downtime,lost or corrupted data,missed sales opportunities,high IT support and maintenance costs,and low customer satisfaction.A year later,InfoWorld Fos06 wrote about the“the sorry state of software quality”reporting that the quality problem had not gotten any better.Today,software quality remains an issue,but who is to blame?Customers blame developers,arguing that sloppy practices lead to low-quality software.Developers blame customers(and other stakeholders),arguing that irrational delivery dates and a continuing stream of changes force them to deliver software before it has been fully validated.,择剥枚根截烬诊揭慰颐维讼接尼萨敌谨馏夏艇耍潞戴愤基梧弄伸堆生脱狡软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,3,Quality,The American Heritage Dictionary defines quality as“a characteristic or attribute of something.”For software,two kinds of quality may be encountered:Quality of design encompasses requirements,specifications,and the design of the system.Quality of conformance is an issue focused primarily on implementation.User satisfaction=compliant product+good quality+delivery within budget and schedule,骂盛劳团请舒噬旧撅类端侄很坦烷奖甩薪喊红访崇瘤靛档囚崔埂胰烷臀薯软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,4,QualityA Philosophical View,Robert Persig Per74 commented on the thing we call quality:Quality.you know what it is,yet you dont know what it is.But thats self-contradictory.But some things are better than others,that is,they have more quality.But when you try to say what the quality is,apart from the things that have it,it all goes poof!Theres nothing to talk about.But if you cant say what Quality is,how do you know what it is,or how do you know that it even exists?If no one knows what it is,then for all practical purposes it doesnt exist at all.But for all practical purposes it really does exist.What else are the grades based on?Why else would people pay fortunes for some things and throw others in the trash pile?Obviously some things are better than others.but whats the betterness?.So round and round you go,spinning mental wheels and nowhere finding anyplace to get traction.What the hell is Quality?What is it?,廖辟骚冻瀑渺康下摸囱匪菠央琉老层坦践乙揣逼夹度绍膳虹井绳俐巷煽熄软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,5,QualityA Pragmatic View,The transcendental view argues(like Persig)that quality is something that you immediately recognize,but cannot explicitly define.The user view sees quality in terms of an end-users specific goals.If a product meets those goals,it exhibits quality.The manufacturers view defines quality in terms of the original specification of the product.If the product conforms to the spec,it exhibits quality.The product view suggests that quality can be tied to inherent characteristics(e.g.,functions and features)of a product.Finally,the value-based view measures quality based on how much a customer is willing to pay for a product.In reality,quality encompasses all of these views and more.,砰超择名婴玛抵移俄福妇街冉膨魏龄确制窖涕咏铱损茵的薯磋叶劣泌桔港软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,6,Software Quality,Software quality can be defined as:An effective software process applied in a manner that creates a useful product that provides measurable value for those who produce it and those who use it.This definition has been adapted from Bes04 and replaces a more manufacturing-oriented view presented in earlier editions of this book.,晴遏忍厕呈调垄娱拎湍熔锐挎蛛蔼粱扯网它惯饥瓦声稳射遁语丙稻民没升软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,7,Effective Software Process,An effective software process establishes the infrastructure that supports any effort at building a high quality software product.The management aspects of process create the checks and balances that help avoid project chaosa key contributor to poor quality.Software engineering practices allow the developer to analyze the problem and design a solid solutionboth critical to building high quality software.Finally,umbrella activities such as change management and technical reviews have as much to do with quality as any other part of software engineering practice.,嘴卸畸澄璃沧愈顾衷督侦拦搁厦屡叮挎赎丛滇舍胳问膊偿御道背琳靶朵哎软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,8,Useful Product,A useful product delivers the content,functions,and features that the end-user desiresBut as important,it delivers these assets in a reliable,error free way.A useful product always satisfies those requirements that have been explicitly stated by stakeholders.In addition,it satisfies a set of implicit requirements(e.g.,ease of use)that are expected of all high quality software.,豫矾皇缴捞使琴描腾簧枚应颂皆能碰税糟滚攒烫胚赎瑞补性磷胚懂马措躁软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,9,Adding Value,By adding value for both the producer and user of a software product,high quality software provides benefits for the software organization and the end-user community.The software organization gains added value because high quality software requires less maintenance effort,fewer bug fixes,and reduced customer support.The user community gains added value because the application provides a useful capability in a way that expedites some business process.The end result is:(1)greater software product revenue,(2)better profitability when an application supports a business process,and/or(3)improved availability of information that is crucial for the business.,臻侨穗碾剔亭谭亏盐霉妖陋榷偏哩碰歧挑烦痘廷殃倚主陀舟嫁蛀晃咸骨杰软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,10,Quality Dimensions,David Garvin Gar87:Performance Quality.Does the software deliver all content,functions,and features that are specified as part of the requirements model in a way that provides value to the end-user?Feature quality.Does the software provide features that surprise and delight first-time end-users?Reliability.Does the software deliver all features and capability without failure?Is it available when it is needed?Does it deliver functionality that is error free?Conformance.Does the software conform to local and external software standards that are relevant to the application?Does it conform to de facto design and coding conventions?For example,does the user interface conform to accepted design rules for menu selection or data input?,错鸣难梯酱捻碘公狠决傣弱需卿棱绷蚀胜保蓝锌哗诞匈贯坟笔拇缸电浴馆软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,11,Quality Dimensions,Durability.Can the software be maintained(changed)or corrected(debugged)without the inadvertent generation of unintended side effects?Will changes cause the error rate or reliability to degrade with time?Serviceability.Can the software be maintained(changed)or corrected(debugged)in an acceptably short time period.Can support staff acquire all information they need to make changes or correct defects?Aesthetics.Most of us would agree that an aesthetic entity has a certain elegance,a unique flow,and an obvious“presence”that are hard to quantify but evident nonetheless.Perception.In some situations,you have a set of prejudices that will influence your perception of quality.,栋爹贝撤巩畴裳芜筑落盟级怂阉愚碱齿拯醉皮鳃觉句轻形削乓点姻鹤拒咀软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,12,Other Views,McCalls Quality Factors(SEPA,Section 14.2.2)ISO 9126 Quality Factors(SEPA,Section 14.2.3)Targeted Factors(SEPA,Section 14.2.4),压听请施潦丛辞欲耶善遗辉枚穿三墅顷博柏储锈茅蕾忍奔痰包躺庄昧俗盟软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,13,The Software Quality Dilemma,If you produce a software system that has terrible quality,you lose because no one will want to buy it.If on the other hand you spend infinite time,extremely large effort,and huge sums of money to build the absolutely perfect piece of software,then its going to take so long to complete and it will be so expensive to produce that youll be out of business anyway.Either you missed the market window,or you simply exhausted all your resources.So people in industry try to get to that magical middle ground where the product is good enough not to be rejected right away,such as during evaluation,but also not the object of so much perfectionism and so much work that it would take too long or cost too much to complete.Ven03,席挚诫趾壁潜猿掉奢簿菏舟曹达宠蕉弗几苫捶绞放坑砰摆胎虐防防光爽痘软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,14,“Good Enough”Software,Good enough software delivers high quality functions and features that end-users desire,but at the same time it delivers other more obscure or specialized functions and features that contain known bugs.Arguments against“good enough.”It is true that“good enough”may work in some application domains and for a few major software companies.After all,if a company has a large marketing budget and can convince enough people to buy version 1.0,it has succeeded in locking them in.If you work for a small company be wary of this philosophy.If you deliver a“good enough”(buggy)product,you risk permanent damage to your companys reputation.You may never get a chance to deliver version 2.0 because bad buzz may cause your sales to plummet and your company to fold.If you work in certain application domains(e.g.,real time embedded software,application software that is integrated with hardware can be negligent and open your company to expensive litigation.,宦竹吁沽念组鹤褂蠢邢被踏引簿比瞥乎常凄蝇灸你访糙淬橇监埂树遵养吉软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,15,Cost of Quality,Prevention costs includequality planningformal technical reviewstest equipmentTrainingInternal failure costs includereworkrepairfailure mode analysisExternal failure costs arecomplaint resolutionproduct return and replacementhelp line supportwarranty work,弘琶么稚零颠牺蚁运缚汛迂湿哭数簧踩僚锈掉童再谱罐残酌烃害愈棠丫翁软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,16,Cost,The relative costs to find and repair an error or defect increase dramatically as we go from prevention to detection to internal failure to external failure costs.,棱攘莆说季青技报义劝磅苔赌抿足采渴否拄持需睬镭乌攒墨特卵籽凡组怪软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,17,Quality and Risk,“People bet their jobs,their comforts,their safety,their entertainment,their decisions,and their very lives on computer software.It better be right.”SEPA,Chapter 1Example:Throughout the month of November,2000 at a hospital in Panama,28 patients received massive overdoses of gamma rays during treatment for a variety of cancers.In the months that followed,five of these patients died from radiation poisoning and 15 others developed serious complications.What caused this tragedy?A software package,developed by a U.S.company,was modified by hospital technicians to compute modified doses of radiation for each patient.,寒获床袋桑椒呀芍润樟国天综疑缩恰畔痘货缅庞箩勾酸咱偏音浇牢宜监绘软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,18,Negligence and Liability,The story is all too common.A governmental or corporate entity hires a major software developer or consulting company to analyze requirements and then design and construct a software-based“system”to support some major activity.The system might support a major corporate function(e.g.,pension management)or some governmental function(e.g.,healthcare administration or homeland security).Work begins with the best of intentions on both sides,but by the time the system is delivered,things have gone bad.The system is late,fails to deliver desired features and functions,is error-prone,and does not meet with customer approval.Litigation ensues.,亮塘德轰康嗅盲脐妆魔教递雕翼饱礼烘辊美旁抉娃策涯诈卢兜例辅富锰死软件工程-实践者的研究方法chapter_11软件工程-实践者的研究方法chapter_11,These slides are designed to accompany Software Engineering:A Practitioners Approach,7/e(McGraw-Hill,2009).Slides copyright 2009 by Roger Pressman.,19,Quality and Security,Gary McGraw comments Wil05:“Software security relates entirely and completely to quality.You must think about security,reliability,availability,dependabilityat the beginning,in the design,architecture,test,and coding phases,all through the software life cycle process.Even pe