COCOMO

Not to be confused with Kokomo.

The Constructive Cost Model (COCOMO) is a procedural software cost estimation model developed by Barry W. Boehm. The model parameters are derived from fitting a regression formula using data from historical projects (61 projects for COCOMO 81 and 163 projects for COCOMO II).

History

The constructive cost model was developed by Barry Boehm in the late 1970s[1] and published in Boehm's 1981 book Software Engineering Economics[2] as a model for estimating effort, cost, and schedule for software projects. It drew on a study of 63 projects at TRW Aerospace where Boehm was Director of Software Research and Technology. The study examined projects ranging in size from 2,000 to 100,000 lines of code, and programming languages ranging from assembly to PL/I. These projects were based on the waterfall model of software development which was the prevalent software development process in 1981.

References to this model typically call it COCOMO 81. In 1995 COCOMO II was developed and finally published in 2000 in the book Software Cost Estimation with COCOMO II.[3] COCOMO II is the successor of COCOMO 81 and is claimed to be better suited for estimating modern software development projects; providing support for more recent software development processes and was tuned using a larger database of 161 projects. 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 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:

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 (note: the values listed below are from the original analysis, with a modern reanalysis[4] producing different values):

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 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 COCOMOs

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
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:

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.

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:-

See also

References

  1. ↑ Stutzke, Richard. "Software Estimating Technology: A Survey". Retrieved 9 Oct 2016.
  2. ↑ Boehm, Barry (1981). Software Engineering Economics. Prentice-Hall. ISBN 0-13-822122-7.
  3. ↑ Barry Boehm, Chris Abts, A. Winsor Brown, Sunita Chulani, Bradford K. Clark, Ellis Horowitz, Ray Madachy, Donald J. Reifer, and Bert Steece. Software Cost Estimation with COCOMO II (with CD-ROM). Englewood Cliffs, NJ:Prentice-Hall, 2000. ISBN 0-13-026692-2
  4. ↑ "COCOMO: Not worth serious attention". The Shape of Code. 19 May 2016. Retrieved 4 November 2016.

Further reading

External links


This article is issued from Wikipedia - version of the 11/14/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.