Software Engineering
Outline of this presentation
• Constructive Cost Modeling (Constructive Cost Model)
• 3 COCOMO Models
http://en.wikipedia.org/wiki/COCOMO
• Project Characteristics
• Some Assumptions
• Basic COCOMO Model
– Equations
– When Should You Use It
– Limitations
– Examples
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Constructive Cost Modeling
• COCOMO is one of the most widely used software
estimation models in the world
• It was developed by Barry Boehm in 1981
• COCOMO predicts the effort and schedule for a
software product development based on inputs
relating to the size of the software and a number
of cost drivers that affect productivity
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Constructive Cost Modeling
3 COCOMO Models :
• COCOMO has three different models
that reflect the complexity:
1. the Basic Model
2. the Intermediate Model
3. and the Detailed Model
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Constructive Cost Modeling
Project Characteristics
• Organic Mode
– Small to medium size product development
– developed in a familiar, in-house & stable
environment,
– similar to the previously developed projects
– relatively small and requires little innovation
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Constructive Cost Modeling
Project Characteristics
• Semidetached Mode
– Team members have an intermediate level
of experience with related systems.
– Perhaps a mixture of experienced and
inexperienced people.
– Parts of the project may require rigorous
interfaces.
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Constructive Cost Modeling
Project Characteristics
• Embedded Mode
– tight, inflexible constraints and interface
requirements
– The product requires great innovation
– Product must operate within a strongly coupled
complex of H/W, S/W, regulations, and
operational procedures.
– Tighter requirements and more inflexible
scheduling
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Constructive Cost Modeling
Some Assumptions
• Primary cost driver is the number of Delivered
Source Instructions (DSI) developed by the
project (LOC/KLOC)
• COCOMO estimates assume that the project will
enjoy good management by both the developer
and the customer
• Assumes the requirements specification is not
substantially changed after the plans and
requirements phase
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Constructive Cost Modeling
Basic COCOMO Model
• Basic COCOMO model estimates the software
development effort using only a single
predictor variable (size in DSI) and three
software development modes
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Constructive Cost Modeling
Basic COCOMO Model: Equations
Mode
Effort
Schedule
Man-Month / Person-Month
Organic
1.05
E=2.4*(KDSI)
1.12
Semidetached E=3.0*(KDSI)
Embedded
1.20
E=3.6*(KDSI)
Month
0.38
TDEV=2.5*(E)
0.35
TDEV=2.5*(E)
0.32
TDEV=2.5*(E)
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Constructive Cost Modeling
When Should You Use It
• Basic COCOMO is good for quick, early, rough
order of magnitude estimates of software
costs
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Constructive Cost Modeling
Limitation of Basic COCOMO Model
• Its accuracy is necessarily limited because
of its lack of factors which have a significant
influence on software costs
• The Basic COCOMO estimates are within a
factor of 1.3 only 29% of the time, and
within a factor of 2 only 60% of the time
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Constructive Cost Modeling
An Example
• We have determined our project fits the
characteristics of Semi-Detached mode
• We estimate our project will have 32,000
Delivered Source Instructions. Using the
formulas, we can estimate:
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Constructive Cost Modeling
An Example
• Effort = 3.0*(32)
1.12
• Schedule = 2.5*(146)
= 146 Man-Months
0.35
= 14 Months
• Productivity / Man Month
= 32,000 DSI / 146 MM
= 219 DSI/MM
• Average Staffing / Month
= 146 MM /14 M
= 10 Man
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Constructive Cost Modeling
An Example
Bila sebuah proyek dikelompokkan kedalam
organic mode project diperkirakan akan
menghasilkan 32,000 DSI,
maka:
PM = 2.4 * (32) 1.05
= 91 p.m.
Dari nilai PM yang diperoleh dapat dihitung
berapa lama proyek akan diselesaikan
TDEV = 2.5 (91) 0.38
= 14 bulan
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Constructive Cost Modeling
An Example
Bila sebuah proyek dikelompokkan kedalam
embedded mode project diperkirakan akan
menghasilkan 128,000 DSI, maka:
PM = 3.6 (128) 1.20
= 1216 p.m.
Dari nilai PM yang diperoleh dapat dihitung
berapa lama proyek akan diselesaikan
TDEV = 2.5 (1216) 0.32
= 24 bulan
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