Cost Estimation

1
Cost Estimation

• Estimates based on LOC

2
Boehm's COCOMO

• Software Engineering Economics
• Prentice-Hall c1981
• type COCOMO in a search engine - many www sites

3
COnstructive COst MOdel

• Basic
• macro - overview of whole project with one metric
  of KSLOC
• Intermediate
• multiplicative adjustment factors
• Detailed
• applying model to each phase

4
Modes of Software Development

• Organic
• detached, often batch
• Semidetached
• e.g. transaction processing
• Embedded
• e.g. os kernel

5
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

6
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

7
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

9
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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Productivity

• The productivity is defined as LOC per time unit.
• The usual units are LOC/Programmer-Day
• Divide final size of project by total
  programmer-days of effort for the whole software
  development

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TTYP1

• What is the effort, productivity, staffing and
  delivery time for an application project that
  takes 175K loc?
• What is the effort, productivity, staffing and
  delivery time for a system project that take 400K
  loc?

13
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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Putnam's Cost Estimation Model

• macro-estimation model that uses LOC
• relationship between cost and the amount of time
  available for the development effort.
• The model supports the 'mythical man-month' idea

15
Putnam's Model

• Uses the Rayleigh Curve
• Shows Instantaneous Programmer-power vs Time
• Empirically verified on other projects

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Rayleigh Curve

• The rayleigh curve is a product of at times e
  raised to the -bt squared
• The at dominates at first giving a steep rise and
  then the negative power of e lowers the value
  slowly

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Rayleigh Curve

• y instantaneous programmer-power
• K total lifecycle cost ( in programmer-years)
• t time from beginning of project
• td delivery time
• e 2.71828...

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Software Equation

• There must be a relationship between the
  lifecycle development effort, the development
  time and the size of the project.
• This relationship is given in the Software
  Equation

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Software Equation

• Ss CK1/3 td4/3
• where
• Ss is the estimated size of the software system
• K is the total lifecycle effort in
  programmer-years
• C is the technology constant
• td is the development time (in years)

B is special skills factor P is productivity
parameter
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Putnam by spread-sheet
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Thursday, Oct 19

• Function Point Estimation
• Read Pressman pp 440-444 and 653-654
• Read SOS sec 4.4.4
• PLQ Wednesday