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Software Estimating Technology:A Survey

Richard Stutzke

Crosstalk, May96

text pp204-215

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Cost Estimation

An estimate of the effort and duration, associated costs of equipment, travel and

training and the rationale for the calculations

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Problem

“The estimator must estimate the effort (person-hours) and duration (calendar-day) for the project to enable managers to determine improtant business measures such as product costs, return on investment, and time to market.”

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Recommendation

If you are involved with cost estimation, I recommend the following book

Tom DeMarco, Controlling Software Projects, Yourdon Press, NY c1982

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Definition of Estimate (DeMarco)

Default:– "An estimate is the most optimistic prediction

that has a non-zero probability of coming true" Proposed:

– "An estimate is a prediction that is equally likely to be above or below the actual result"

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Estimates should not become goals

DeMarco argues that the estimation and the management decision about pricing or goals should be separate.

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Estimate

cost

estimate price

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Parametric Cost Estimation LOC models

– Boehm's COCOMO– Putnam's Model (SLIM)

non-LOC models– Function Points

combination– COCOMO2

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Prediction Formulas

E=X

>1

<1

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Boehm's COCOMO

Software Engineering Economics – article (1983) pp216-233 in text

Software Engineering Economics – (book) Prentice-Hall c1981

type COCOMO in a search engine - many www sites

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COnstructive COst MOdel

Basic– macro - overview of whole project with one

metric of KSLOC Intermediate

– multiplicative adjustment factors Detailed

– applying model to each phase

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Modes of Software Development

Organic– detached, often batch

Semidetached– e.g. transaction processing

Embedded– e.g. os kernel

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Programmer Effort

Application Programs– PM = 2.4 * (KDSI)1.05

Utility Programs– PM = 3.0 * (KDSI)1.12

Systems Programs– PM = 3.6 * (KDSI)1.20

Note A’s in text are different from later versions of COCOMO

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Example for effort Size Appl Util Sys 5K 13.0 18.2 24.8 10K 26.9 39.5 57.1 15K 41.2 62.2 92.8 20K 55.8 86.0 131.1 25K 70.5 110.4 171.3 30K 85.3 135.3 213.2 35K 100.3 160.8 256.6 40K 115.4 186.8 301.1 45K 130.6 213.2 346.9 50K 145.9 239.9 393.6

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Development Time (Months)

Application Programs– TDEV = 2.5 * (PM) 0.38

Utility Programs– TDEV = 2.5 * (PM) 0.35

Systems Programs– TDEV = 2.5 * (PM) 0.32

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Example for development time

size appl util sys 5K 6.63 6.90 6.99 10K 8.74 9.06 9.12 15K 10.27 10.62 10.66 20K 11.52 11.88 11.90 25K 12.60 12.97 12.96 30K 13.55 13.93 13.91 35K 14.40 14.80 14.75 40K 15.19 15.59 15.53 45K 15.92 16.33 16.25 50K 16.61 17.02 16.92

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Average Staffing Levels

Calculate by dividing PM by TDEV

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Example for staffing levels

size appl util sys 5K 1.96 2.63 3.55 10K 3.08 4.37 6.26 15K 4.01 5.87 8.71 20K 4.84 7.23 11.02 25K 5.60 8.51 13.21 30K 6.30 9.72 15.33 35K 6.97 10.87 17.39 40K 7.60 11.98 19.39 45K 8.20 13.05 21.35 50K 8.79 14.09 23.27

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COCOMO Effort Multipliers

product attributes – required reliability 0.75 - 1.40– data-base size 0.94 - 1.16– product complexity 0.70 - 1.65

computer attributes– execution time constraint 1.00 - 1.66– main storage constraint 1.00 - 1.56– virtual machine volatility 0.87 - 1.30– computer turnaround time 0.87 - 1.15

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The Cocomo 2.0 Software Cost Estimation Model

Barry Boehm, etal

See web pages