Chapter 19 Process Quality

1. Chapter 19 Process Quality

2. outline • Then meaning of process quality • Process measurement • COQ • Failure costs, Appraisal costs, Prevetion Costs • Simplifications of COQ- Failure costs, Appraisal costs • A/FR: The Appraisal/Failure Ratio • The calculation of A/FR 山东大学计算机学院

3. 取决于 取决于 need need need Process measure Quality of program Quality of process The way you work Better program Change the way you work Know your process Measure the quality of process 山东大学计算机学院

4. Quality Measurement • It concerns: • The volume of products produced; • The quality of the products; • The time and resources required. • In this class, only the perspective of defect injection and defect removal are being addressed. 山东大学计算机学院

5. What not introduced? • Requirement • Usability • Compatibility • Interface • …… 山东大学计算机学院

6. Defect-Removal Paradox • One interesting phenomenon: Defect-removal rates decline as product quality improves. • It seems like a paradox, but it’s natural. • Clearly true for reviewing and testing; • Less true for compiling. 山东大学计算机学院

7. Defect-Removal Strategy • Defects can divided into two classes: • Involve only one module • Involve interactions among the modules • Defect –removal strategy: • Strive to develop modules of the highest possible quality; • Do thorough inspections of all the modules interfaces and interactions. • Inspect the requirements to ensure that all of the important capablities are properly understood, designed, and implemented; 山东大学计算机学院

8. Defect-Removal Strategy • Inspect the system and program design against the requirements to ensure that it properly address all the key requirements. • Do exhaustive unit testing after the code has been inspected; • Do comprehensive intergration testing; • Do thorough system testing. • The first step is up to you,but most important! 山东大学计算机学院

9. Cost of Quality---COQ • Balance the time spent and quality of products produced. • COQ (cost measured in time) • Failure costs of quality （纠错成本）All the costs of fixing defects. • Fixing defects time; Debugging time; redesigning, retesting or recomiling; • Appraisal costs of quality（评价成本）all the work to assess the product to see if it has defects. • Code reviewing time; compiling and testing time; • Exclude the time spent on defects fixing in above phase. • Prevention costs of quality （预防成本）modify the process to avoid injecting defects • Do analysing time; process of development work to improve the requirements, design, or implementation; • Building prototypes. 山东大学计算机学院

10. Simplifying the calculation of COQ • PSP counts all compile time as failure costs. • Even include some defect-free compile time. • PSP counts all test time as failure costs. • PSP counts all review time as appraisal costs. • Appraisal COQ: sum of all review time as a percentage of total development time; • Failure COQ: sum of all compile and test time as a percentage of total development time; • See the example of table 19.1 山东大学计算机学院

11. A/FR-Appraisal/Failure Ratio • Simpler calculate: code review time/(compile time+test time); • It measures the relative amount of time spent finding defects before the first compile. • You should attempt to achieve A/FR of 2 or more. • Why? See figure 19.1-19.6 • Improving the product quality; • Saving test time. 山东大学计算机学院

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13. How to achieve A/FRs above 2.0 ? • Putting more time on code reviewing; • This will not improve program quality!!! • It is important to productively use review time in finding defects. • Code review with high quality. • For frequently missed defects. • Insert appropriate steps in checklist. • Take more time,find more defects,increase A/FR 山东大学计算机学院

14. Improving review rates • Continue check the defect data • Continue update your personal checklist. • How? 山东大学计算机学院

15. Calculating the true COQ • Break the review, compile, and test times to their respective appraisal and failure time. • C=CF+CA; R=RF+RA; T=TF+TA. • Appraisal COQ=100*(RA +CA +TA)/totaltime • Failure COQ=100*(RF +CF +TF)/totaltime. • See example in table 19.1 and table 19.3. • To use this method,you need a stopwatch! 山东大学计算机学院

16. Summary • Process measurement; • COQ and its calculation; • Meaning of A/FR. • The value of A/FR should be equal to or more than 2.0. • Why? • How? 山东大学计算机学院

17. assignment • Determine the value of A/FR for all the programs you have written. • Show the relations of A/FR and test defects/KLOC like figure 19.1 山东大学计算机学院

18. Chapter 20A Personal Commitment to Quality

19. outline • Why you should establish quality as your highest priority? • Personal life purposes. • Just for discussion, no content for examination. 山东大学计算机学院

20. The important of quality • Quality of software will be critically important to your employers and to your customers • Software defects can cause economic damage and even physical harm. • Airplane,auto,air traffic, factories, power plant, nuclear power plants. 山东大学计算机学院

21. The increasing risk of poor quality • Any defect in a small part of a large program could potentially cause serious problem. • Safety system also made of software. • Most common cause of problem is simple oversights and goofs. • Feel simple mistakes will be simple find. • The quality of large system depend on small programs. 山东大学计算机学院

22. Making a commitment to quality • To decided that quality is important • To establish the goal of producing defect-free program • To manage our fallibility(失误). • Care enough to continue doing. 山东大学计算机学院

23. Your personal objectives • What do you want from your life? • This is a big problem! • One way is to have status or power. • Is it good? • No answer! 山东大学计算机学院

24. The rewards of accomplishment • Whatever you build ,quality will be key! • Sloppy job will destroy your pride in the work and it will limit your satisfaction with life. • When do quality work, you will be proud. • So ask yourself the question: • “Do I want to feel proud of what I do?” 山东大学计算机学院

25. Challenge yourself to do superior work and you will be surprised at what you can accomplish. 山东大学计算机学院

26. The end Thanks very much!