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Defect Removal Effectiveness Model

Defect Removal Effectiveness Model. Product Quality is Based on Many Items People Training Tools Activities Process Our software development Process should include Defect Prevention Activities Defect Removal Activities. Defect Prevention & Removal. Defect Prevention Activities

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Defect Removal Effectiveness Model

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  1. Defect Removal Effectiveness Model • Product Quality is Based on Many Items • People • Training • Tools • Activities • Process • Our software development Process should include • Defect Prevention Activities • Defect Removal Activities

  2. Defect Prevention & Removal • Defect Prevention Activities • Reuse of Proven, Existing Material • “Defensive” Software Activities: • Well Documented Requirements and Tracking • Business Process and Usage • User Background • Constraints • Well Documented Design and Tracking • Data Flow • Functions • Inter-related Structures • Error Conditions • Well Commented Source Code • Pre and Post Condition Statements in Source Code • Use Available Programming Constructs • Switch vs multiple ifs • Functions vs Multi-Parameter Subroutine Calls • Abstract class and Interface (java) • Configuration and Change Management

  3. Defect Prevention & Removal • Defect Removal Activities • Pre-coding • Reviews and Inspections • Coding • Reviews and Inspections • Unit Test • Post-coding • Functional Test and fixes • Component Test and fixes • System and Regression Test and fixes • Post-release • Customer Support and fixes

  4. (Testing) Reviews and Inspections • Mostly Applied to Code and Pre-code Materials • Involves one or more people other than the author • Requires certain amount of preparation • Examining the material for completeness , correctness, and consistency • Compare against the material from the previous activity(s) • Analyzethe correctness of the result produced by the activity • Focused on discovering defects • Activity is relatively static or non-execution oriented • Requires recording of problems found • Requires the follow up on fixes of the problems and on inspection results

  5. (Testing) Machine Testing • Applied to Machine Executable Material • Code • On-line Help • Messages and Information Boxes • Other User Interface • Performed by Author(s) and Mostly Others • Has Several Major Steps • Test planning and preparation • Development of test scenarios and test cases • Running the tests • Recording the problems found and managing the fixes • Analysis of the test results

  6. More on Testing Requirements & Design Specs Executable Code, Help,Messages Etc. Test Scenarios & Test Cases How do these three sets interact and relate ? - size : amount of material - overlaps : coverage of specs by executables by tests

  7. White Box and Black Box Testing Executables more than specs Executables less than specs code requirement test test Use White Box : Coverage Oriented after looking at the inside of the actual executables Use Black Box : Functionally Oriented without looking at the inside of the actual executables .VS. Most of Us Need Both

  8. A Test Case Example Test Case # : Purpose : Any Pre-Condition : Input(s) : Expected Output(s) : Any Post-Condition : Test Results : Test DateTest PersonActual ResultProblem Description Fix Status

  9. Defect RemovalActivitymodel Number of defects found and removed in this activity Number of errors introduced in this activity Number of defects upon exit an activity Number of defects upon entering an activity + Defect Removal Activity How may we want to represent defect removal effectiveness (DRE) ? DRE = (# defects found & removed)/[(#defects on entry)+(#defects introduced)] = 1 (best) to 0 (worst)

  10. A Complete Set of Defect Removal Activities Software Activities Hi-lev Design Lo-lev Design Code/ Unit Test case System Test cases Req Gath ……………. Defect Removal Total n n Req Insp 1,1 1. n n n Des Insp 2,1 2,2 2. . . . . . n n C Test i.1 i,j Sys Test Total n N n .2 .1 Where n i,j is # of error removed by removal activity i on artifact j

  11. Defect Removal Effectiveness Metrics Defect Removal Activity, i, Effectiveness or DRA E may be : i 1) n / N i . 2) n / (( Sum (n ) where j < or = i) - (Sum (n ) where m< or = i-1) ) . j i . m . Note that Customer Found Problems and “Unfound” Errors are not included in the metrics discussion.

  12. An Example with Numbers Software Activities Hi-lev Design Lo-lev Design Code/ Unit T System Test Total Req Gath ……………. Defect Removal 45 45 Req Insp 12 31 43 Des Insp . . . . . 24 4 C Test n Sys Test i,j Total 95 85 340 Where n is # of error removed by removal i on activity j i,j

  13. Numerical Example • High Level Design Inspection Effectiveness Metrics: • 1. 43 / 340 = .126 • 2. 43 / ( (95+85) – (45) ) = 43/135 = .31 • (*Remember not all potential defects are accounted for )

  14. Is There Any Possibility of Projecting Field Problems ? • Possibly with 2 “Big” Assumptions • Let MP = problems found in all the inspections and reviews • Let PTR = problems found in all the tests • Let Q = problems to be found by customers (after release in the field) • Let UP = defects never found as problems • Let TD = total defects of the software • So TD= MP + PTR + Q + UP • *** Assumption 1 : UP = 0 • So TD = MP + PTR + Q • *** Assumption 2 : Effectiveness of Inspections = Effectiveness of Tests • So MP/TD = PTR / (TD-MP) • Or MP/PTR = TD/(TD-MP) • Or MP/PTR = (MP+PTR+Q) / ((MP+PTR+Q) - MP) • Or MP/PTR = (MP+PTR+Q) / (PTR + Q) • Or MP*(PTR + Q) = PTR * (MP+PTR+Q) • Or MP*PTR + MP*Q = PTR*MP +PTR*PTR +PTR*Q • Or MP*Q = PTR*PTR + PTR*Q • Or Q *(MP –PTR) = PTR *PTR • Or Q = (PTR * PTR) / (MP – PTR) ** a possible predictor of Post Release Quality !

  15. Defining Defect Removal Effectiveness as before • Effectiveness of Inspections & Reviews, E1: E1 = MP / TD • Effectiveness of Testing , E2: E2 = PTR / (TD – MP) your thoughts? Check text book page 174’s discussion on μ, and higher the value of μ=MP/PTR implies more effectiveness is the front-end defect removal. Consider MP =2, PTR = 1, and TD = 4. then μ = MP/PTR = 2 /1 = 2 - - - says “front end more effective?” E1 = 2/4 = 1/2 E2 = 1/ (4 -2) = 1/2 E1 = ½ = E/2 - - - - same effectiveness !? What do you think about μ ?

  16. An Interesting Note from the Book (p175-177) • Using the same previous notations and the assumption that MP/TD = PTR / (TD-MP) and μ = MP/PTR, Q = TD/ μ2 • So if we can project total defects and know μ , then we can also project Q. try manipulating from the previous Q= PTR2 / (MP-PTR)

  17. Defect removal effectiveness and CMM • It’s been estimated (by Capers Jones) that defect removal effectiveness differs by different levels of process capability maturity levels: • Level 1: 85% • Level 2: 89% • Level 3: 91% • Level 4: 93% • Level 5: 95% Caution: Not clear what “%” really is here; thus not clear what removal effectiveness really means here. Discussion?

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