COCOMO

About 3 pages (1,018 words)

Questions on this topic? Just ask!

This article or section is in need of attention from an expert on the subject.

WikiProject Computer science may be able to help recruit one.
If a more appropriate WikiProject or portal exists, please adjust this template accordingly.

In 1981, Barry Boehm designed COCOMO to give an estimate of the number of man-months it will take to develop a software product. References to this model typically call it COCOMO 81. In 1990, a new model called COCOMO II appeared. Generally, references to COCOMO before 1995 refer to the original COCOMO, references after 1995 refer to COCOMO II. The need for the new model came as software development technology moved from mainframe and overnight batch processing to desktop development, code reusability and the use of off-the-shelf software components. This article refers to COCOMO 81. This "COnstructive COst MOdel" drew on a study of about sixty projects at TRW Aerospace. The study examined programs ranging in size from 2000 to 100,000 lines of code, and programming languages ranging 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

Basic

Basic COCOMO is a form of the COCOMO. COCOMO applies to three classes of software projects:

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 it does not 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, which limits its accuracy.

Intermediate

The Intermediate COCOMO is an extension of the Basic COCOMO, and estimates the programmer time to develop a software product. This extension considers a set of four "cost driver attributes", 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 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 receives a rating on a 6-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.

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 environment		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.