points

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FunctionPointspage1of2

FunctionPoints.

FunctionPointsweredevelopedbyAlbrecht,ngthe

sizeofasoftwaresystemcanbedonemuchearlierusingFPsthanwhenusingLOCbecauFPsonlyrequire

thedetailedrequirementsspecification,onPointsalsoallowustohavea

measureofsizethatis,apparently,independentofimplementationdetail,

interestedinreadingtheoriginalpaperbyAlbrecht,ereferencenumber1.

Thefirstthingtodo,whencountingfunctionpoints,htdefined,

notjustthefivebasicfunctiontypes;externalinputs,externaloutputs,urenquiries,externalfilesandinternal

files,butalsoacomplexityscale;simple,average,andcomplex,ht

waffectivelysayingthatthe

otherwords,hecreatedatableofweightingswherethevalueschangeaccordingtofunctiontypeand

complexity.

FunctiontypeSimple

Weightingfactor

AverageComplex

externalinputs346

externaloutputs457

externalenquiries346

logicalinternalfiles71015

externalinterfacefiles5710

So,eachandeveryfunctionidentifiedintherequirementsisclassifiedbyfunctiontype(eabove)andthen

classifiedbycomplexity(simple,averageorcomplex).Then,eachandeveryfunctionismultipliedbyitsown

weightingfactor–thederivednumbersaresummedtogethertogiveafirstapproximationofoverallsizeofthe

rstapproximationistermedtheUnadjustedFunctionPointCount(UFPC).Thefinalcalculation

ofthesizeofthesystem–inFunctionPoints-takestheUFPCandadjustsitupordownbyasmuchas35%.

Thefollowingtwotablesareudtodetermineafunction'hfunction,twooutofthethree

determinants(#files,#recordtypes,#dataelements)

determinantvaluesarethenaddedtogethertogivethedeterminantscore,whichistranslatedusingthecond

tablebelow.

Functiontype

Determinant

▼#files#recordtypes#dataelements

rnal

inputs

0-12>21-45-15>15

rnal

outputs

0-12-341-56-19>19

rnal

enquiries

Computeboththeexternalinputandexternaloutputcomponents

-uwhicheveristhegreater.

rnal

interfacefiles

12-5>51-1920-50>50

cal

internalfiles

12-5>51-1920-50>50

Score►

123123123

Determinant

Score

Complexity

Rating

2-3Simple

4Average

5-6complex

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FunctionPointspage2of2

Forexample,anexternalinputthatreferenced3filesandsixteendataelementswouldhaveadeterminantscore

of3+3=6,resultinginacomplexityratingof‘complex’.

Albrechtoriginallylefttheasssmentofthecomplexityofeachfunctiontopersonaljudgement–afactor

oftheabovetablesreducesthesubjectivityinthe

calculationofFunctionPointsconsiderably.

InadditiontotheUnadjustedFunctionPointCount,Albrechtalsosaidthatthesizeofthesystemwasalso

htidentifiedfourteensystemcharacteristics

DatacommunicationsDistributeddataprocessing

PerformanceHeavilyudconfiguration

TransactionrateOn-linedataentry

End-urefficiencyOn-lineupdate

ComplexprocessingRe-usability

InstallationeaOperationea

MultiplesitesFacilitatechange

Eachofthefourteencharacteristicsisassignedascorebadonthefollowingdegreeofinfluence.

DegreeofInfluenceScore

Notprent/noinfluence0

Incidental/insignificantinfluence1

Moderateinfluence2

Averageinfluence3

Significantinfluence4

Esntial/verystronginfluence5

Thefourteenscoresarethenaddedtogethertogivewhatiscalledthe'TechnicalComplexityFactor'forthe

system,ht,fromthedatahehad,saidthattheTCFcouldadjustthesizeofthesystem

alculatethatadjustmentfactorisshownhere:

adjustmentfactor=0.65+(0.01xTCF),

whereTCFliesintherange0→(14x5=70).

HavingcalculatedtheadjustmentfactoritmustnowbemultipliedbytheearlierderivedUnadjustedFunction

PointCounttoarriveatthefinalcalculationofthenumberofFPsinthesystem.

mple,theconvolutedwayof

derivingthecomplexityofeachfunction,orthelackofindependencebetweenthefourteensystem

etheproblems,FunctionPointshaveproven,overtheyears,to

beaverypopularwayofestimatingthesizeofasystem.

Reference

1Albrecht,A.J.,‘Measuringapplicationdevelopmentproductivity’,inProcedingsSHARE-GUIDE

Symposium,Monterey,CA.,IBM,1979.