Defect Prevention

Insanity is doing the same thing over and overand expecting different results Rita Mae Brown

What is Defect Prevention?Corrective and Preventive Actions (Galin)The activities involved in identifying defects or potential defects and preventing them from being introduced into a product (Zahran)A defect prevention program focuses on those process areas that are the greatest sources of trouble, whether methods, technology, procedures or training (Humphrey)

Software Process ModelsDefect PreventionCMM Level 5 Key Process AreaCausal Analysis and Resolution CMMI Support Process Area at Maturity Level 5Problem Resolution ProcessSPICE Support Process (SUP.8) Not specifically mentioned in ISO9000

How can we prevent defects?Design and development methods:Formal methodsObject-oriented programmingRequirements engineeringPrototypingDiagramming techniquesUnified Modelling Language (UML). but we need to look at our output

Why defect prevention?Substantial fraction of budget fixing defectsExamined probability of recovering when defects are found Probability of introducing errors when fixing errors is higher than introducing errors when writing original codeFinancial motivation

W.E. Deming:What is needed in improvement of the process, by reduction of variation, or by change of level, or both. Study of the sources of product, upstream, gives powerful leverage on improvement.

Principles of Defect PreventionProgrammers evaluate their own errorsFeedback is essentialNo such thing as panaceaProcess improvement integral to the processProcess improvement takes time to learn

PI integral to the process

Effort and discipline in defect prevention; of equal weight to detection and fixingArchitect and design processConduct inspections and testEstablish baselinesWrite problem reportsTrack and control changes

PI takes time to learnIndividuals need reasonably stable working environmentManaged programConsistent, long-term focusSteady progress

Software Defect Prevention StepsManagement CommitmentDefect ReportingCause AnalysisAction Plan DevelopmentAction ImplementationPerformance TrackingStarting Over

Management CommitmentExplicit commitmentReject or delay project Then people might believe it!Quality improvement actionsEarly fix saves time and resources

Defect ReportingGather informationWhat was the problem?When was it discovered?By whom was it discovered?Categorize each defectRequired for Causal analysisSymptomsRepair Actions

Categories of errorsTechnologicaltools / proceduresOrganisationaldivision of work, communicationHistoricexternal influencesGroup dynamicdistribution of work within project teamIndividualExperience, talentOther causes

Cause AnalysisMeetings should be held to discuss:Problems identified during design inspectionsDefects found during testProblems on first few modulesUser problems after customer releaseFive-eight people at such meetings

Cause / Effect Diagram

Action Plan DevelopmentCause of defect?Major cause categories?What steps can we recommend for preventing errors?Priority of each actionIf defect was missed at previous stage (e.g. inspection), then not only should the defect cause be examined, but also the reason why the previous stage missed the defect!

Action implementationAction teamPriority actionsManagement involvementCause analysis teamsTrack implementation progressRecognition of people who implement

Performance TrackingAction logged and trackedStatus reported periodicallyFollow-up reportsAging statisticsOpen item listsPriority hot lists

Prevention feedbackAwareness of effortsInvolves training programs for new tools and methodsSeminars on the most recent experiences and plansProject kick-off meeting for each project

Process changes for Defect PreventionKick-off meetingUpdating process databaseCause analysis review meetingReview process databaseAction tracking system PrioritizingFeedback system

Starting overBack into the improvement cycle making sure that we have continuous improvement within Defect Prevention.

Software Defect PreventionManagement CommitmentDefect ReportingCause AnalysisAction Plan DevelopmentAction ImplementationPerformance TrackingStarting Over

End notesWhere to startRoles of tools and technologyCost-benefit