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Estimation for Software Projects

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Software Project Planning

• Estimation

• Scheduling

• Risk Analysis

• Quality Management Planning

• Change Management Planning

2

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Estimation

• Estimation determines how much money effort resources and time itwill take to !uild a s"ecific system or "roduct

• #he software team first estimates

 – #he work to !e done

 – #he resources re$uired – #he time that will ela"se from start to finish

• #hen they esta!lish a "roject schedule that

 – %efines tasks and milestones

 – &dentifies who is res"onsi!le for conducting each task 

 – S"ecifies the inter'task de"endencies

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Categories of Resources

Human Resources-  )um!er re$uired-  Skills re$uired-  *eogra"hical location

Development Environment-  Software tools-  Com"uter hardware-  )etwork resources

Reusable Software Components-  +ff'the'shelf com"onents-  ,ull'e-"erience com"onents-  Partial'e-"erience com"onents-  )ew com"onents

#he

Project

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Estimation of Project Cost and Effort

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Project Estimation +"tions

• +"tions for achie/ing relia!le cost and effort estimates

01 %elay estimation until late in the "roject we should !e a!le toachie/e 04 accurate estimates after the "roject is com"lete1

21 5ase estimates on similar "rojects that ha/e already !eencom"leted

31 6se relati/ely sim"le decom"osition techni$ues to generate "roject cost and effort estimates

(1 6se one or more em"irical estimation models for software costand effort estimation

• +"tion 70 is not "ractical !ut results in good num!ers

• +"tion 72 can work reasona!ly well !ut it also relies on other "roject influences !eing roughly e$ui/alent

• +"tions 73 and 7( can !e done in tandem to cross check each other 

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Project Estimation A""roaches

• %ecom"osition techni$ues

 – #hese take a 9di/ide and con$uer9 a""roach

 – Cost and effort estimation are "erformed in a ste"wise fashion

 !y !reaking down a "roject into major functions and relatedsoftware engineering acti/ities

• Em"irical estimation models

 – +ffer a "otentially /alua!le estimation a""roach if the historical

data used to seed the estimate is good

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%ecom"osition #echni$ues

• 5efore an estimate can !e made and decom"osition techni$uesa""lied the "lanner must

 – 6nderstand the sco"e of the software to !e !uilt

 –

*enerate an estimate of the software;s si

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A""roaches to Software Si

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Pro!lem'5ased Estimation

01 Start with a !ounded statement of sco"e

21 %ecom"ose the software into "ro!lem functions that can each !eestimated indi/idually

31 Com"ute an >+C or ,P /alue for each function

(1 %eri/e cost or effort estimates !y a""lying the >+C or ,P /alues toyour !aseline "roducti/ity metrics e?g? >+C@"erson'month or,P@"erson'month1

1 Com!ine function estimates to "roduce an o/erall estimate for theentire "roject

.1 #hen the e-"ected si

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Process'5ased Estimation

01 &dentify the set of functions that the software needs to "erform aso!tained from the "roject sco"e

21 &dentify the series of framework acti/ities that need to !e "erformed

for each function31 Estimate the effort in "erson months1 that will !e re$uired toaccom"lish each software "rocess acti/ity for each function

(1 A""ly a/erage la!or rates i?e? cost@unit effort1 to the effortestimated for each "rocess acti/ity

1 Com"ute the total cost and effort for each function and each

framework acti/ity.1 Com"are the resulting /alues to those o!tained !y way of the >+Cand ,P estimates

#his is the most commonly used of the two estimation techni$ues "ro!lem and "rocess1

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Reconciling Estimates

• #he results gathered from the /arious estimation techni$ues must !ereconciled to "roduce a single estimate of effort "roject duration andcost

• &f widely di/ergent estimates occur further in/estigation is needed – #he sco"e of the "roject is not ade$uately understood or has !een

misinter"reted !y the "lanner 

 – Producti/ity data used for "ro!lem'!ased estimation techni$ues isina""ro"riate for the a""lication o!solete i?e? outdated for the currentorgani

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Em"irical Estimation Models

• Estimation models for com"uter software use em"irically deri/ed

formulas to "redict effort as a function of >+C or ,P

• Resultant /alues com"uted for >+C or ,P are entered into an

estimation model• #he em"irical data for these models are deri/ed from a limited sam"le

of "rojects

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C+C+M+•

Stands for C+nstructi/e C+st M+del• &ntroduced !y 5arry 5oehm in 0=:0 in his !ook Software

Engineering EconomicsD

• 5ecame one of the well'known and widely'used estimation models inthe industry

•

&t has e/ol/ed into a more com"rehensi/e estimation model calledC+C+M+ &&

• C+C+M+ && is actually a hierarchy of three estimation models

• As with all estimation models it re$uires si

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C+C+M+ Model

• Application composition model ' 6sed during the early stages ofsoftware engineering when the following are im"ortant –  Prototy"ing of user interfaces

 – Consideration of software and system interaction

 – Assessment of "erformance

 –

E/aluation of technology maturity• Early design stage model  6sed once re$uirements ha/e !een

sta!ili

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Make@5uy %ecision

• &t is often more cost effecti/e to ac$uire rather than de/elo" software

• Managers ha/e many ac$uisition o"tions – Software may !e "urchased or licensed1 off the shelf 

 – ,ull'e-"erienceD or "artial'e-"erienceD software com"onents may !e

ac$uired and integrated to meet s"ecific needs – Software may !e custom !uilt !y an outside contractor to meet the

 "urchaser;s s"ecifications

• #he make@!uy decision can !e made !ased on the following conditions – Fill the software "roduct !e a/aila!le sooner than internally de/elo"ed

softwareG

 –Fill the cost of ac$uisition "lus the cost of customi

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