cocomo presentation 1
TRANSCRIPT
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Constructive Cost ModelCOCOMO
Adapted from Allan Caine
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Outline
COCOMO in a Coconut-shell Complete Examples
Intermediate COCOMO: Cost DriversAdvantages and Limitations of COCOMO
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COCOMO in a Coconut-shell
bKLOCaE )(=
Where E is the Effort in staff months a and b are coefficients to be determined
KLOC is thousands of lines of code
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The Constants
1.203.6Embedded
1.123.0Semi-detached
1.052.4OrganicbaMode
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The Modes
Organic 2-50 KLOC, small, stable, little innovation
Semi-detached 50-300 KLOC, medium-sized, average
abilities, medium time-constraints
Embedded > 300 KLOC, large project team, complex,
innovative, severe constraints
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Examples
Suppose size is 200 KLOC, Organic
2.4(200)1.05 = 626 staff-months
Semi-Detached
3.0(200)1.12 = 1,133 staff-months
Embedded 3.6(200)1.20 = 2,077 staff-months
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Project Duration
dEcTDEV )(=
Where
TDEV is time for development
c and d are constants to be determined
E is the effort
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Constants for TDEV
0.322.5Embedded
0.352.5Semi-detached
0.382.5OrganicdcMode
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Example
Picking up from the last example, Organic
E = 626 staff months
TDEV = 2.5(626)0.38
= 29 months Semi-detached
E = 1,133
TDEV = 2.5(1133)0.35 = 29 months
Embedded
E = 2077
TDEV = 2.5(2077)0.32 = 29 months
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Average Staff Size
[staff]months][
months]-[staff ===TDEV
ESS
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Productivity
month-staffKLOCmonths]-[staff[KLOC] ===
ESizeP
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Complete Example, Organic
Suppose an organic project has 7.5KLOC,
Effort 2.4(7.5)1.05 = 20 staffmonths
Development time 2.5(20)0.38 = 8 months
Average staff 20 / 8 = 2.5 staff
Productivity 7,500 LOC / 20 staff-months =375 LOC / staff-month
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Complete Example, Embedded
Suppose an embedded project has 50KLOC,
Effort 3.6(50)1.20 = 394 staffmonths
Development time 2.5(394)0.32 = 17months
Average staff 394 / 17 = 23 staff Productivity 50,000 LOC / 394 staff-months
= 127 LOC / staff-month
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Comparison
127375Productivity
232.5Average Staff
178Development
Time
39420Effort (staff-
months)
EmbeddedOrganicItem
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Intermediate COCOMO
Where
E is the effort a and b are constants (as before)
KLOC is thousands of lines of code
C is the effort adjustment factor
CKLOCaEb= )(
New
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Cost Drivers
Intermediate COCOMO introduces CostDrivers
They are used because
they are statistically significant to the costof the project; and
they are notcorrelated to the project size(KLOC).
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Categories
I. Product Attributes II. Computer Attributes
III. Personnel Attributes IV. Project Attributes
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I. Product Attributes
RELYRequired Software Reliability DATAData Base Size
CPLX Product Complexity
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II. Computer Attributes
TIME Execution Time Constraint STORMain Storage Constraint
VIRTVirtual Machine Volatility1
TURN Computer Turnaround Time
1The hardware and software in combination.
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III. Personnel Attributes
ACAPAnalyst CapabilityAEXPApplication Experience
PCAP Programming CapabilityVEXPVirtual Machine Experience1
LEXP Programming LanguageExperience
1
The hardware and software in combination.
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IV. Project Attributes
MODP Modern Programming Practices TOOL Use of Software Tools
SCED Required Development Schedule
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Example
Suppose the following assumptions aremade:
1.17
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Example ..2 So, the nominal amount of staff-months will
be increased by 17% for organic, semi-detached, or embedded projects.
Suppose it is estimated that a project willtake 51 nominal staff-months at $5,000 /staff-month.
The cost: Nominally, $255,000 (51 X $5,000)
Adjusted, $298,350 (51 X $5,000 X 1.17)
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The Proof
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Advantages
Based on history Repeatable
Unique adjustment factors
Has different modes
Works well on similar projects
Highly calibrated Well-documented
Easy to use
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Limitations Ignores requirements volatility
Ignores documentation
Ignores customers skill
Oversimplifies security Ignores software safety
Ignores personnel turnover
Ignores many hardware issues
Personnel experience may be obsolete
Must know the cost drivers Must be able to predict project size
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Final Word
The models are just there to help, notto make the management decisions foryou.
-- Barry Boehm