Chapter 19 Process Quality

山东大学计算机学院 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 Process measure Quality of programQuality of processThe way you work Better programChange the way you work 取决于 Know your process Measure the quality of process need

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  Improving the product quality;  Saving test time.

山东大学计算机学院 12

山东大学计算机学院 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=C F +C A ; R=R F +R A ; T=T F +T A.  Appraisal COQ=100*(R A +C A +T A )/totaltime  Failure COQ=100*(R F +C F +T F )/totaltime.  See example in table 19.1 and table  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

Chapter 20 A Personal Commitment to Quality

山东大学计算机学院 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.

The end Thanks very much!