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1、1Chapter 16n 软件质量保证齐大计控学院吴迪讨论n 软件质量保证为什么重要？3什么是软件质量？n Phil Crosby once said:n The problem of quality management is not what people dont know about it.The problem is what they think they do know.In this regard,quality has much in common with sex.n Everybody is for it.(Under certain conditions,of cour
2、se.)n Everyone feels they understand it.(Even though they wouldnt want to explain it.)n Everyone thinks execution is only a matter of following natural inclinations.(After all,we do get along somehow.)n And,of course,most people feel that problems in these areas are caused by other people.(If only t
3、hey would take the time to do things right.)416.2Elements of SQAn Standards n Reviews and Audits n Testingn Error/defect collection and analysis n Change management n Education n Vendor management n Security management n Safety n Risk management 16.3.1 软件质量保证的任务n 编制项目质量保证计划；n 参与项目的软件过程的描述编写；n 评审软件工程
4、活动，以验证是否符合规定的软件过程；n 审核指定的软件工作产品以验证是否遵守作为软件过程一部分的哪些规定。n 确保根据文档化的规程记录和处理软件工作和工作产品中的偏差；n 记录各种不符合项报告给高层管理人员；6Role of the SQA Group-In Prepares an SQA plan for a project.n The plan identifies evaluations to be performed audits and reviews to be performed standards that are applicable to the project proce
5、dures for error reporting and tracking documents to be produced by the SQA group amount of feedback provided to the software project teamn Participates in the development of the projects software process description.n The SQA group reviews the process description for compliance with organizational p
6、olicy,internal software standards,externally imposed standards(e.g.,ISO-9001),and other parts of the software project plan.8Role of the SQA Group-IIn Reviews software engineering activities to verify compliance with the defined software process.n identifies,documents,and tracks deviations from the p
7、rocess and verifies that corrections have been made.n Audits designated software work products to verify compliance with those defined as part of the software process.n reviews selected work products;identifies,documents,and tracks deviations;verifies that corrections have been maden periodically re
8、ports the results of its work to the project manager.n Ensures that deviations in software work and work products are documented and handled according to a documented procedure.n Records any noncompliance and reports to senior management.nNoncompliance items are tracked until they are resolved.讨论n 如
9、果客户不断改变他想做的事情，是否还有可能评估软件质量？n 为什么软件工程小组与独立的软件质量保证小组的关系经常是紧张的？n 这种紧张关系是否是正常的？1216.3.2 SQA Goals n Requirements quality.The correctness,completeness,and consistency of the requirements model will have a strong influence on the quality of all work products that follow.n Design quality.Every element of t
10、he design model should be assessed by the software team to ensure that it exhibits high quality and that the design itself conforms to requirements.n Code quality.Source code and related work products(e.g.,other descriptive information)must conform to local coding standards and exhibit characteristi
11、cs that will facilitate maintainability.n Quality control effectiveness.A software team should apply limited resources in a way that has the highest likelihood of achieving a high quality result.1416.5 Statistical SQAProduct Product&Process&Processmeasurement.an understanding of how to improve quali
12、ty.Collect information on all defectsFind the causes of the defectsMove to provide fixes for the process1516.5 Statistical SQAn Information about software errors and defects is collected and categorized.n An attempt is made to trace each error and defect to its underlying cause.n Using the Pareto pr
13、inciple(80 percent of the defects can be traced to 20 percent of all possible causes),isolate the 20 percent(the vital few).n Once the vital few causes have been identified,move to correct the problems that have caused the errors and defects.n 已经证明统计软件质量保证技术确实质量提高，某些情况下，软件组织已经去得了每年减少51%缺陷的好成绩。n 统计SQ
14、A 及Pareto 原则的应用可以概括：把时间用在真正重要的地方，但是首先你必须知道什么重要。1716.5.2 Six-Sigma for Software Engineeringn The term“six sigma”is derived from six standard deviations3.4 instances(defects)per million occurrencesimplying an extremely high quality standard.n The Six Sigma methodology defines three core steps:n Define
15、 customer requirements and deliverables and project goals via well-defined methods of customer communicationn Measure the existing process and its output to determine current quality performance(collect defect metrics)n Analyze defect metrics and determine the vital few causes.n Improve the process
16、by eliminating the root causes of defects.n Control the process to ensure that future work does not reintroduce the causes of defects.1916.6 Software Reliabilityn A simple measure of reliability is mean-time-between-failure(MTBF),where MTBF=MTTF+MTTRn The acronyms MTTF and MTTR are mean-time-to-fail
17、ure and mean-time-to-repair,respectively.n Software availability is the probability that a program is operating according to requirements at a given point in time and is defined asAvailability=MTTF/(MTTF+MTTR)x100%2016.6.2Software Safetyn Software safety is a software quality assurance activity that
18、 focuses on the identification and assessment of potential hazards that may affect software negatively and cause an entire system to fail.n If hazards can be identified early in the software process,software design features can be specified that will either eliminate or control potential hazards.讨论和
19、作业n n一个正确的程序还能不可靠吗？一个正确的程序还能不可靠吗？n n一个正确的程序还能不表现高质量吗？一个正确的程序还能不表现高质量吗？n n除了统计错误和缺陷外，还有那些软件特征除了统计错误和缺陷外，还有那些软件特征具有质量意义？具有质量意义？n n给出两个安全性至关重要的计算机控制系统，给出两个安全性至关重要的计算机控制系统，并为每个系统列出至少并为每个系统列出至少33条与软件失效直接相条与软件失效直接相关的灾难。关的灾难。22ISO 9001:2000 Standardn ISO 9001:2000 is the quality assurance standard that app
20、lies to software engineering.n The standard contains 20 requirements that must be present for an effective quality assurance system.n The requirements delineated by ISO 9001:2000 address topics such as n management responsibility,quality system,contract review,design control,document and data control,product identification and traceability,process control,inspection and testing,corrective and preventive action,control of quality records,internal quality audits,training,servicing,and statistical techniques.