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Software QualityLecture 12Lecture 12 Defect Removal Effectiveness

Software Quality

Defect^ Removal

Effectiveness

Defect^ Removal

History ƒ 1960’sƒ 1960 s ƒ “Code and Test”^ methodology ƒ Cost overruns and schedule delaysCost overruns^ and^ schedule^ delays ƒ The only defect^ removal^ step

was^ test

ƒ^ 1970’s^ ƒ^ Formal^ reviews

and^ inspections^ emerged ƒ Productivity and^ quality^ improved

ƒ^ (mid)^ 1980’s^ ƒ^ Defect^ Removal,

Defect^ Removal^ Effectiveness,

and^ Defect Removal Metrics appear in literatureRemoval^ Metrics,^

appear^ in^ literature

Defect^ Removal

Effectiveness

Defect^ Removal

Activity^ Model

Number oferrorsintroduced Number ofdefects

Number ofdefects foundand removed

Number ofdefectsupon exit +^ in thisactivity defectsupon enteringan activity

and removedin this activity

upon exitan activity Defect Removal Activity

Defect^ Removal

Effectiveness

Significance^ of

Defect^ Removal

Effectiveness

ƒ^ It improves the quality of the software producedƒ^ It^ improves^ the

quality^ of^ the^ software

produced

ƒ^ e.g.^ less^ defects

are^ left^ in^ the^ shipped

release

ƒ^ It improves the productivity and scheduling of theIt^ improves^ the

productivity^ and

scheduling^ of^ the

development^ process^ ƒ^ e.g^ it^ ensures^

defects^ are^ found^

early^ and^ less^ time

is^ spent^ fixing k^ f^ l^

h mistakes^ found^ late

in^ the^ process

ƒ^ It^ reduces^ the

cost^ of^ development ƒ e g if productivity improves and scheduling does not fall behindƒ e.g. if productivity^ improves^ and

scheduling^ does^ not

fall^ behind then^ costs^ go^ down.

Defect^ Removal

Effectiveness

General^ Equation

For^ Effectiveness^ Defects Found By StageDefects

Found By Stage Defect Removal Effectiveness =

Defects Present At Stage

x 100%

where:^ ƒ^ ‘Defects^ Present

At^ Stage’^ are^ defects

at^ entry^ to^ stage^ p

lus g^

y^ g^ p defects^ injected^ during

stage,^ and^ counted

as:

-^ Defects^ Found^ +^ Defects

Not^ Found ƒ^ ‘Defects not found’ is determined at later stagesƒ^ Defects^ not^ found

is^ determined^ at^

later^ stages ƒ^ Must^ account^ for

where^ defects^ should

have^ been^ caught

(I.e.

defect^ must^ have^

existed^ in^ that^ stage

to^ be^ counted^ against effectiveness^ of^ stage)

Defect^ Removal

Effectiveness

Definitions^ ƒ^ Defects can be

injected^ into software artifacts at any point

ƒ^ Defects^ can^ be

injected^ into^ software

artifacts^ at^ any

point

in^ software^ development ƒ Defects can be^

removed^ at any stage after they have been

Defects^ can^ be^

removed^ at^ any

stage^ after^ they

have^ been

injected^ ƒ^ For^ example,^ requirements

defects^ could^ be^ removed

during^ the f^ f^ d^ ll l^

ld b^ d requirements^ stage

or^ if^ not^ found^ till

later^ could^ be^ removed during^ design,^ implementation,

testing,^ etc

ƒ^ The^ sooner^ a

defect^ is^ found

the^ better^ http://www.pieas.edu.pk/umarfaiz/cis

Defect^ Removal

Effectiveness

Defect^ Injection

and^ Removal

by^ Stage

ƒ^ The detailed mechanics of defect injection and removal atƒ^ The^ detailed^

mechanics^ of^ defect

injection^ and^ removal

at

each^ step^ of^ the

development^ process

is^ shown

Defect^ Removal

Effectiveness

Defect^ Matrix^ ƒ^ We need to construct a defect matrix by cross classifyingƒ^ We^ need

to^ construct^ a^

defect^ matrix^ by

cross‐classifying

defect^ data^ in^ terms

of

ƒ^ Development^ phases

in^ which^ the^ defects

are^ found^ (and p^ p^

removed) ƒ Development^ phases

in^ which^ the^ defects

are^ injected.^ http://www.pieas.edu.pk/umarfaiz/cis

Defect^ Removal

Effectiveness

Defect^ Effectiveness

Metric

ƒ^ We can measure the effectiveness of a given step S usingƒ^ We^ can^ measure

the^ effectiveness

of^ a^ given^ step

,^ S,^ using

the^ following^ formula: where step S would bewhere^ step^ S^ would

be

ƒ^ High‐level^ design

inspection^ effectiveness ƒ^ Code^ inspection

effectiveness ƒ^ Unit^ test^ effectiveness ƒ^ etc

Defect^ Removal

Effectiveness

Example^ of^ Defect

Removal^ Metric

ƒ^ Calculate the high level design inspection effectivenessƒ^ Calculate^ the

high‐level^ design

inspection^ effectiveness

Answer:Defects^ removed

at^ l0^ =^730 Defects existing on step entry (escapes from requirements phase)Defects existing on^ step^ entry^ (escapes

from^ requirements

phase)

=^122 Defects^ injected^ in

current^ phase^ =^859 IE(I1)^ [730/(122 859]

100%^ 74%

IE(I1)^ =^ [730/(122+859]

x100%^ =^ 74%

Defect^ Removal

Effectiveness

Example^ of^ Defect

Removal^ Metric

ƒ^ Calculate the component test effectiveess designƒ^ Calculate^ the

component^ test

effectiveess^ design

inspection^ effectiveness Answer:Defects removed at l1 = 729Defects^ removed

at^ l1^ =^729 Defects existing on^ step^ entry^ (escapes

from^ requirements

phase

and^ I0)^ =^122 +^859

‐^730 =^251

D f^ i j^ d i^

h^939 Defects^ injected^ in

current^ phase^ =^939 IE(I1)^ =^ [729/(251+939]

x100%^ =^ 61%

Defect^ Removal

Effectiveness

Example^ of^ Defect

Removal^ Metric

ƒ^ Calculate the code inspection effectivenessƒ^ Calculate^ the

code^ inspection

effectiveness

Answer:Defects^ removed

at^ l1^ =^1095 Defects existing on step entry (escapes from requirements phaseDefects existing on^ step^ entry^ (escapes

from^ requirements

phase,

I0^ and^ I1)^ =^122 +^ 859+

‐^730 ‐729=^461

Defects^ injected^ in

current^ phase^ =^1537 IE(I1)^ [1095/(461 1537]

100%^ 55%

IE(I1)^ =^ [1095/(

+1537]^ x100%^ =^ 55%

Defect^ Removal

Effectiveness

Example^ of^ Defect

Removal^ Metric

ƒ^ Calculation of the unit component and test effectivenessƒ^ Calculation^ of

the^ unit,^ component

and^ test^ effectiveness

(Alternate^ approach)Answer:Answer:For^ the^ testing^ phases,

the^ defect^ injection

(bad^ fixes)^ is^ usually

a

small^ number.^ In^ such

cases,^ effectiveness

can^ be^ calculated

by^ an

alternative method (Dunn's formula or Jones's second formula)alternative^ method

(Dunn's^ formula^ or

Jones's^ second^ formula) TE^ (UT)^ =^ 332/[332^ +^387

+^111 +^ 81]^ x^ 100%^ =^ 36% TE^ (CT)^ =^ 387/[387^ +^111

+81]^ x^ 100%^ =^ 67% TE (ST) = 111/[111 + 81] x 100% = 58%TE^ (ST)^ =^ 111/[111^ +^ 81]

x^ 100%^ =^ 58%

Defect^ Removal

Effectiveness

Example^ of^ Defect

Removal^ Metric

ƒ^ Calculation overall test effectiveness and defect removalƒ^ Calculation^ overall

test^ effectiveness

and^ defect^ removal

effectivenessAnswer:Answer:Overall^ Test^ Effectiveness:TE^ =^332 +^387

+111/[332^ +^387 +^111

+^ 81]^ x^ 100%^ =^ 91% f^ l^ ffDefect^ Removal^ EffectivenessDRE^ =^ [1‐81/3465]^

=^ 97.7%