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Encyclopedia > COCOMO

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In 1981, Barry Boehm designed COCOMO to give an estimate of the number of man-months it will take to develop a software product. Barry W. Boehm is known for many contributions to software engineering. ... This does not cite its references or sources. ... Software, consisting of programs, enables a computer to perform specific tasks, as opposed to the physical components of the system (hardware). ...


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 model, 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, a Californian automotive and IT company, that Northrop Grumman acquired in late 2002. The study examined programs ranging in size from 2000 to 100,000 lines of code, and programming languages ranging from assembly to PL/I. TRW Incorporated was an American corporation involved in a number of businesses, mostly defense-related, but including automotive supply and credit reporting. ... The Northrop Grumman Corporation (NYSE: NOC) is an aerospace and defense conglomerate that is the result of a 1994 merger between Northrop and Grumman. ... Source lines of code (SLOC) is a software metric used to measure the amount of code in a software program. ... Assembly may refer to the following things: In politics, any body meeting together to discuss matters, a parliament or a legislative assembly such as the French revolutionary Legislative Assembly, or a body more designed to mediate between otherwise independent bodies, such as the United Nations General Assembly. ... PL/I (Programming Language One, pronounced pee el one) is an imperative computer programming language designed for scientific, engineering, and business applications. ...


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.

Contents

Basic

Basic COCOMO is a form of the COCOMO model. 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=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

The Intermediate COCOMO is an extension of the Basic COCOMO model, 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: Basic COCOMO is a form of the COCOMO model. ...

  • 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.

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 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=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 with Basic COCOMO.


See also

The ability to accurately estimate the time/cost taken for a project to come to its successful conclusion has been 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 [1], . It gives an estimate of the number of person-months it will take to staff systems engineering resources on hardware and software projects. ... Software engineering economics is the economics of the software industry. ... Cost overrun is defined as excess of actual cost over budget. ... The Putnam model is an empirical software effort estimation model. ...

Further reading

  • Barry Boehm. Software engineering economics. Englewood Cliffs, NJ:Prentice-Hall, 1981. ISBN 0-13-822122-7
  • Barry Boehm, et al. Software cost estimation with COCOMO II (with CD-ROM). Englewood Cliffs, NJ:Prentice-Hall, 2000. ISBN 0-13-026692-2
  • Stan Malevanny. Case Study: Software Project Cost Estimates Using COCOMO II Model, 2005.
  • Kemerer, Chris F. (May, 1987). An Empirical Validation of Software Cost Estimation Models. Communications of the ACM.

Barry W. Boehm is known for many contributions to software engineering. ... Barry W. Boehm is known for many contributions to software engineering. ...

External links

  • COCOMO Overview
  • COCOMO II website
  • COCOMO II online calculator
  • COCOMO SCORM Cost Model
  • NASA basic COCOMO online calculator (Broken)

  Results from FactBites:
 
Tactical Leadership : Weblog (1427 words)
The CoCoMo model was developed by reviewing many projects, from small to large, embedded to interactive, and an equation was developed that best fit the empirical data.
CoCoMo also predicted that the project could have been completed in about a year with a little more than three people.
Using CoCoMo on historical data is a nice confirmation of the model.
COCOMO (3342 words)
Consider the form of the estimating equations (as explained in the COCOMO Overview).
COCOMO II is defined using intermediate calculations, but the COCOMO 81 models let you choose between the Intermediate mode and the Detailed mode.
COCOMO II.1998 was renamed to COCOMO II.1999 and then to COCOMO II.2000, so all of those models are identical.
  More results at FactBites »


 

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