GEF 492'14 COCOMO II

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GEF 492.14COCOMO II
Royal Military College of Canada Electrical and
Computer Engineering

• Dr. Terry Shepard
• shepard_at_rmc.ca
• 1-613-541-6000 ext. 6031

Other sources - van Vliet, 7.3.6 - other
professors at RMC
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COCOMO II

• COnstructive COst MOdel
• We will consider the Post-Architecture submodel
• Estimation requires detail that is only available
  at the post architecture stage
• There are also Application Composition and Early
  Design submodels in COCOMO II)

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COCOMO is an algorithmic model

• COnstructive COst Model
• e.g. effort ?(x1, x2,... xn)
• Why use an algorithmic model?
• Gives a firm basis for planning
• makes a more believable case to management,
  customers when a proposal is unrealistic
• Allows for sensitivity analysis
• Gives a plan with which to judge progress
• Is a basis for keeping plans up to date

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COCOMO History

• The original COCOMO is introduced in Dr. Barry
  Boehm's textbook Software Engineering Economics. 
  This model is now generally called "COCOMO 81
• Early papers describing COCOMO II published
• The first calibration of COCOMO II is released by
  Dr. Boehm, and named "COCOMO II.1997
• The book Software Cost Estimation with COCOMO II
  (Dr. Barry Boehm, et al) is published to document
  how to apply the latest estimation model. 
• Most of Boehms original book on Software
  Engineering Economics is still applicable to
  modern software projects.

• 1981
• 1995-6
• 1997
• 2000

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COCOMO II assumptions

• primary cost driver kDSI (1000s delivered source
  instructions)
• may be different from the total kSLOC (1000s
  source LOC ) developed
• cost estimates limited to
• direct development activities (similar to the
  calculation of velocity )
• direct charged labour includes analysts, PM,
  designers
• estimates are in terms of person months, so
  conversion to s can be fully burdened, not
  burdened, or somewhere in between
• customer developer play well together
• need an architecture that is stable
• Factors are not manipulated or misunderstood. 5
  types

Scaling Factors Product Factors Platform Factors
Personnel Factors Project Factors
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Fundamental Logic
Early Design Post Architecture
The work required to build the system measured in
person-months
The time required to build the system measured in
months
Some measure of the size of the system

• Effort a Size b

• Duration c Size d

Multiplier
Exponent

• Staffing Effort/Duration or does it?

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Effort

• Measure effort in Person Months
• PMNS a x ( ?i1..17 EMi ) x Size b
• where
• a 2.94 (calibrated from 161 projects)
• b 1.01 0.01 x S SFj
• EMi - effort multipliers (i 1 to 17 range from
  .75 1.67)
• SFj - exponential scale factors (j 1 to 5
  range from 0 - 5)
• NS - implies nominal schedule

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Exponential Scale Factors

• PREC Precedentedness
• FLEX Development flexibility
• RESL Architecture/risk resolution
• TEAM Team cohesion
• PMAT Process Maturity

(See handouts)
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Scaling Factors each range from 0 to 5

• cause an exponential cost increase

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Scaling Factors
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Effort Multipliers

• Product Factors
• RELY Reliability Required
• DATA Database Size
• CPLX Product Complexity
• RUSE Required Usability
• DOCU Documentation Needs
• Platform Factors
• TIME Execution time constraints
• STOR Main storage constraints
• PVOL Platform volatility

• Personnel Factors
• ACAP Analyst capability
• PCAP Programmer capability
• APEX Application experience
• PLEX Platform experience
• LTEX Language tool exp
• PCON Personnel continuity
• Project Factors
• TOOL Use of software tools
• SITE Multi-site development
• SCED Req Development schedule

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Effort Multipliers

• Product factors

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Effort Multipliers

• Platform factors

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Effort Multipliers

• Personnel factors

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Effort Multipliers

• Project factors

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Effort Multipliers (Post-Architecture)
every 1 mo.
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Effort Multipliers (Post-Architecture)
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Calibration

• The values of all of the factors are derived from
  real projects
• context of those projects matters
• The resulting model produces estimates within
  30 of the actuals 52 of the time for effort.
• Calibrating the COCOMO II Post-Architecture
  Model, Bradford Clark, Sunita Devnani-Chulani and
  Barry W. Boehm, International Conference on
  Software Engineering, 1998, pp. 477-480

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What is the maximum variation?

• PMNS a x ? EMi x Size (1.01 0.01 x S SF
  )

j
0.14 to 346
1.01 to 1.26
for 1000kSLOC
10001.01 1071 10001.26 6900
.14 x 1000 140
346 x 1000 346,000
An eleven year project requiring 346,000 PMs
means an average staffing level of 2621
persons -not clear that the model is accurate at
the extremes
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Aside
Exponential Scale Factor
kLOC1.26
Estimated Effort Required
kLOC1.13
kLOC1.01
1000
5000
Where are most University projects on this scale?
Size of Program in kLOC
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Development Time

• assume nominal schedule
  schedules can be compressed stretched (75 -
  160)
• time TDEV c x (PMNS)d
• where
• c 3.67
• d 0.28 0.2 x b - 1.01
• b 1.01 0.01 x S SFj (j 1 to 5)

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Wait a sec...
If total effort in person months is
What is this?
TDEV c x (PMNS)d
Turns out there is also an optimal development
time (which is also based on project size and
other factors)
Now can calculate staff required

• Staffing Effort/Duration

Notes Staffing curve is not flat
COCOMO II assumes 152 person hours/month
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Compress/stretch schedules

• What if it has to be faster?
• What if it can be slower?

Going faster increases effort
Nominal
Going slower does nothing!
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What else can we do?

• Option analysis
• eg. What is the effect of hiring more skilled
  workers?
• eg. What is the effect of contracting out a
  portion?
• example in next few slides simplified analysis
  of the tradeoff between keeping development at
  multiple locations vs. renting new office space
  so everyone can work in the same location

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Example
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Sample Option Analysis

• 20kSLOC
• all factors are nominal except staffing which is
  at multiple locations
• Question if cost per staff is 6000 per month,
  and new facilities will cost 10000 per month, is
  it worthwhile to move to the new facilities?

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Sample Option Analysis

• PMNS 2.94 x 1.25 x 20 (1.16) 118.7 PM
• TDEV 3.67 x (PMNS).31 17 months
• Staffing 8.34 9 pers
• Total cost 17 9 6000 918,000

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Sample Option Analysis

• PMNS 2.94 x 20 (1.16) 94.96 PM
• TDEV 3.67 x (PMNS).31 15 months
• Staffing 6.37 7 pers
• Total cost 15 7 6000 630,000
  cost of new facilities
• 1510,000 150,000
  --------------
• 780,000
• Savings of 138,000, less the cost of the move