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1、1Chapter 16nSoftware Quality AssuranceSoftware Engineering: A Practitioners Approach, 7/e by Roger S. Pressman2Comment on QualityThe 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:Every
2、body is for it. (Under certain conditions) Everyone feels they understand it. (Even though they wouldnt want to explain it.) Most people feel that problems in these areas are caused by other people. (If only they would take the time to do things right.)3Elements of SQA(SQA-Software Quality Assurance
3、)nStandards nReviewsnTestingnError/defect analysis nChange management nSecurity management nRisk management 4Role of SQA GroupnPrepares an SQA plan for a project. The plan identifies:evaluations to be performedreviews to be performedstandards that are applicable to the projectprocedures for error re
4、porting and trackingdocuments to be produced by SQA groupfeedback provided to software project teamnParticipates in the development of the projects software process description. The SQA group reviews the process description for compliance(服从) with organizational policy, internal software standards,
5、externally standards (e.g. ISO-9001), and other parts of software project plan.nReviews software engineering activities to verify compliance with the defined software process. nEnsures that deviations(偏离偏离) in software work and work products are documented and handled according to a documented proce
6、dure.5SQA GoalsnRequirements quality. The correctness, completeness, and consistency of the requirements model will have a strong influence on the quality of all work products. nDesign quality. Every element of the design model should be assessed by the software team to ensure that it exhibits high
7、quality and that the design itself conforms to requirements.nCode quality. Source code and related work products must conform to local coding standards and exhibit characteristics that will facilitate maintainability.nQuality control effectiveness. A software team should apply limited resources in a
8、 way that has the highest likelihood of achieving a high quality result.6Statistical SQAnInformation about software errors and defects is collected and categorized(第一步：故障分类)nAn attempt is made to trace each error and defect to its underlying(潜在) cause (e.g., non-conformance to specifications, design
9、 error, violation(违反) of standards, poor communication with the customer)(第二步：原因分析)nUsing the Pareto principle (80 percent of the defects can be traced to 20 percent of all possible causes), isolate the 20 percent (the vital few)(第三步：原因确认)nOnce the vital few causes have been identified, move to corr
10、ect the problems that have caused the errors and defects(第四步：故障排除)7Software Reliability and AvailabilitynA simple measure of reliability is mean-time-between-failure (MTBF平均故障间隔时间), where MTBF = MTTF + MTTRMTTF and MTTR are mean-time-to-failure(平均无故障时间)and mean-time-to-repair(平均修复时间) respectively.nS
11、oftware availability(软件可用性) is the probability that a program is operating according to requirements at a given point in time and is defined asAvailability = MTTF/(MTTF + MTTR) x 100% 8ISO 9001:2000 StandardnISO 9001:2000 is the quality assurance standard that applies to software engineering. nThe s
12、tandard contains 20 requirements that must be present for an effective quality assurance system. nThe requirements delineated(描绘) by ISO 9001:2000 address topics such as management responsibility, quality system, contract review, design control, document and data control, product identification and traceability, process control, testing, corrective and preventive action, control of quality records, internal quality audits, training, servicing, and statistical techniques.
