COCOMO

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COCOMO is a model designed by Barry Boehm to give an estimate of the number of man-months it will take to develop a software product.

This "COnstructive COst MOdel" is based on a study of about sixty projects at TRW, a Californian automotive and IT company, acquired by Northrop Grumman in late 2002. The programmes examined ranged in size from 2000 to 100,000 lines of code, and programming languages used ranged from assembly to PL/I.

COCOMO consists of a hierarchy of three increasingly detailed and accurate forms.

Basic COCOMO - is a static, single-valued model that computes software development effort (and cost) as a function of program size expressed in estimated lines of code.
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.
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.

1 Basic
2 Intermediate
3 See also
4 Further reading
5 External links

[edit] Basic

Basic COCOMO is a form of the COCOMO model. COCOMO may be applied to three classes of software projects. These give a general impression of the software project.

Organic projects - are relatively small, simple software projects in which small teams with good application experience work to a set of less than rigid requirements.
Semi-detached projects - are intermediate (in size and complexity) software projects in which teams with mixed experience levels must meet a mix of rigid and less than rigid requirements.
Embedded projects - are software projects that must be developed within a set of tight hardware, software, and operational constraints.

The basic COCOMO equations take the form

E=a_b(KLOC)^b_b

D=c_b(E)^d_b

P=E/D

where E is the effort applied in person-months, D is the development time in chronological months, KLOC is the estimated number of delivered lines of code for the project (expressed in thousands), and P is the number of people required. The coefficients a_b, b_b, c_b and d_b are given in the following table.

   Software project    a_b      b_b      c_b      d_b
  
   Organic             2.4     1.05    2.5     0.38
   Semi-detached       3.0     1.12    2.5     0.35
   Embedded            3.6     1.20    2.5     0.32

Basic COCOMO is good for quick, early, rough order of magnitude estimates of software costs, but its accuracy is necessarily limited because of its lack of factors to account for differences in hardware constraints, personnel quality and experience, use of modern tools and techniques, and other project attributes known to have a significant influence on software costs.

[edit] Intermediate

The Intermediate COCOMO is an extension of the Basic COCOMO model, and is used to estimate the programmer time to develop a software product. This extension considers a set of "cost driver attributes" that can be grouped into four major categories, each with a number of subcategories:

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 engineer 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 is rated on a 6-point scale that ranges from "very low" to "extra high" (in importance or value). Based on the rating, an effort multiplier is determined from the table below. The product of all effort multipliers results in an 'effort adjustment factor (EAF). Typical values for EAF range from 0.9 to 1.4.

Product attributes
Cost Drivers	Ratings
Cost Drivers	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
Hardware attributes
Run-time performance constraints			1.00	1.11	1.30	1.66
Memory constraints			1.00	1.06	1.21	1.56
Volatility of the virtual machine envionment		0.87	1.00	1.15	1.30
Required turnabout time		0.87	1.00	1.07	1.15
Personnel attributes
Analyst capability	1.46	1.19	1.00	0.86	0.71
Applications experience	1.29	1.13	1.00	0.91	0.82
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
Project attributes
Use of software tools	1.24	1.10	1.00	0.91	0.82
Application of software engineering methods	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...

E=a_i(KLOC)^(b_i).EAF

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 EAF is the factor calculated above. The coefficient a_i and the exponent b_i are given in the next table.