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The COnstructive COst MOdel (COCOMO) is an algorithmic Software Cost Estimation Model developed by Barry Boehm. The ability to accurately estimate the time and/or cost taken for a Project to come in to its successful conclusion is a serious problem for software engineers. Barry W Boehm is known for his many contributions to software engineering The model uses a basic regression formula, with parameters that are derived from historical project data and current project characteristics. In statistics regression analysis is a collective name for techniques for the modeling and analysis of numerical data consisting of values of a Dependent variable (response

Contents

Overview

COCOMO was first published in 1981 Barry J. Boehm's Book Software engineering economics[1] as a model for estimating effort, cost, and schedule for software projects. Barry W Boehm is known for his many contributions to software engineering It drew on a study of 63 projects at TRW Aerospace where Barry Boehm was Director of Software Research and Technology in 1981. TRW Incorporated was an American Corporation involved in a number of businesses mostly defense-related but including Automotive, Aerospace and Barry W Boehm is known for his many contributions to software engineering The study examined projects ranging in size from 2000 to 100,000 lines of code, and programming languages ranging from assembly to PL/I. Source lines of code ( SLOC) is a Software metric used to measure the size of a software program by counting the number of lines in the text of the program's PL/I ("Programming Language One" ˌpiːˌɛlˈwʌn is an imperative computer Programming language designed for scientific engineering These projects were based on the waterfall model of software development which was the prevalent software development process in 1981. The waterfall model is a sequential Software development process (a process for the creation of software in which development is seen as flowing steadily downwards

References to this model typically call it COCOMO 81. In 1997 COCOMO II was developed and finally published in 2001 in the book Software Cost Estimation with COCOMO II[2]. COCOMO II is the successor of COCOMO 81 and is better suited for estimating modern software development projects. It provides more support for modern software development processes and an updated project database. A software development process is a structure imposed on the development of a software product 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.

COCOMO consists of a hierarchy of three increasingly detailed and accurate forms. The first level, Basic COCOMO is good for quick, early, rough order of magnitude estimates of software costs, but its accuracy is limited due to its lack of factors to account for difference in project attributes (Cost Drivers). Intermediate COCOMO takes these Cost Drivers into account and Detailed COCOMO additionally accounts for the influence of individual project phases.

Basic COCOMO

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. COCOMO applies to three classes of software projects:

The basic COCOMO equations take the form

E=ab(KLOC)bb
D=cb(E)db
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 ab, bb, cb and db are given in the following table. 

   Software project    ab      bb      cb      db
  
   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 COCOMO

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:

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.

Cost Drivers Ratings
Very Low Low Nominal High Very High Extra High
Product attributes
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=ai(KLoC)(bi). 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 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

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.

Projects using COCOMO

See also

References

  1. ^ Barry Boehm. Ohloh is a Website which provides a Web services suite and Online community platform that aims to map the landscape of Open source software The ability to accurately estimate the time and/or cost taken for a Project to come in to its successful conclusion is a serious problem for software engineers. The Constructive Systems Engineering Cost Model (COSYSMO was created by Ricardo Valerdi while at the University of Southern California Center for Software Engineering The software industry comprises businesses involved in the development, maintenance and publication of Computer software. Cost overrun is defined as excess of actual Cost over Budget. The Putnam model is an empirical software effort estimation model SEER-SEM the System Evaluation and Estimation of Resources - Software Estimating Model is a software project estimation model widely used within defense military / aerospace Barry W Boehm is known for his many contributions to software engineering Software engineering economics. Englewood Cliffs, NJ:Prentice-Hall, 1981. ISBN 0-13-822122-7
  2. ^ Barry Boehm, et al. Barry W Boehm is known for his many contributions to software engineering Software cost estimation with COCOMO II (with CD-ROM). Englewood Cliffs, NJ:Prentice-Hall, 2000. ISBN 0-13-026692-2

Further reading

External links

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