The Constructive Cost Model (COCOMO) is an algorithmic software cost estimation model developed by Barry W. Boehm. The model uses a basic regression formula with parameters that are derived from historical project data and current as well as future project characteristics.
Basic COCOMO compute software development effort (and cost) as a function of program size. Program size is expressed in estimated thousands of source lines of code (SLOC, KLOC).
COCOMO applies to three classes of software projects:
- Organic projects – “small” teams with “good” experience working with “less than rigid” requirements
- Semi-detached projects – “medium” teams with mixed experience working with a mix of rigid and less than rigid requirements
- Embedded projects – developed within a set of “tight” constraints. It is also combination of organic and semi-detached projects.(hardware, software, operational, …)
The basic COCOMO equations take the form
- Effort Applied (E) = ab(KLOC)bb [ man-months ]
- Development Time (D) = cb(Effort Applied)db [months]
- People required (P) = Effort Applied / Development Time [count]
where, KLOC is the estimated number of delivered lines (expressed in thousands ) of code for project. The coefficients ab, bb, cb and db are given in the following table:
Basic COCOMO is good for quick estimate of software costs. However it does not account for differences in hardware constraints, personnel quality and experience, use of modern tools and techniques, and so on.
Intermediate COCOMO computes software development effort as function of program size and a set of “cost drivers” that include subjective assessment of product, hardware, personnel and project attributes. This extension considers a set of four “cost drivers”, each with a number of subsidiary attributes:-
- Product attributes
- Required software reliability
- Size of application database
- Complexity of the product
- Hardware attributes
- Run-time performance constraints
- Memory constraints
- Volatility of the virtual machine environment
- Required turnabout time
- Personnel attributes
- Analyst capability
- Software engineering capability
- Applications experience
- Virtual machine experience
- Programming language experience
- Project attributes
- Use of software tools
- Application of software engineering methods
- Required development schedule
Each of the 15 attributes receives a rating on a six-point scale that ranges from “very low” to “extra high” (in importance or value). An effort multiplier from the table below applies to the rating. The product of all effort multipliers results in an effort adjustment factor (EAF). Typical values for EAF range from 0.9 to 1.4.
|Very Low||Low||Nominal||High||Very High||Extra High|
|Required software reliability||0.75||0.88||1.00||1.15||1.40|
|Size of application database||0.94||1.00||1.08||1.16|
|Complexity of the product||0.70||0.85||1.00||1.15||1.30||1.65|
|Run-time performance constraints||1.00||1.11||1.30||1.66|
|Volatility of the virtual machine environment||0.87||1.00||1.15||1.30|
|Required turnabout time||0.87||1.00||1.07||1.15|
|Software engineer capability||1.42||1.17||1.00||0.86||0.70|
|Virtual machine experience||1.21||1.10||1.00||0.90|
|Programming language experience||1.14||1.07||1.00||0.95|
|Application of software engineering methods||1.24||1.10||1.00||0.91||0.82|
|Use of software tools||1.24||1.10||1.00||0.91||0.83|
|Required development schedule||1.23||1.08||1.00||1.04||1.10|
The Intermediate Cocomo formula now takes the form:
where E is the effort applied in person-months, KLoC is the estimated number of thousands of delivered lines of code for the project, and EAFis the factor calculated above. The coefficient ai and the exponent bi are given in the next table.
Software project ai bi Organic 3.2 1.05 Semi-detached 3.0 1.12 Embedded 2.8 1.20
The Development time D calculation uses E in the same way as in the Basic COCOMO.
Detailed COCOMO incorporates all characteristics of the intermediate version with an assessment of the cost driver’s impact on each step (analysis, design, etc.) of the software engineering process.
The detailed model uses different effort multipliers for each cost driver attribute. These Phase Sensitive effort multipliers are each to determine the amount of effort required to complete each phase. In detailed cocomo,the whole software is divided in different modules and then we apply COCOMO in different modules to estimate effort and then sum the effort
In detailed COCOMO, the effort is calculated as function of program size and a set of cost drivers given according to each phase of software life cycle.
A Detailed project schedule is never static.
The Six phases of detailed COCOMO are:-
- plan and requirement.
- system design.
- detailed design.
- module code and test.
- integration and test.
- Cost Costructive Model