Putnam model

Putnam model

The Putnam model is an empirical software effort estimation model.cite book | last = Putnam
first = Lawrence H.
coauthors = Ware Myers
title = Five core metrics : the intelligence behind successful software management
publisher = Dorset House Publishing
date = 2003
month = September
isbn = 0-932633-55-2
] As a group, empirical models work by collecting software project data (for example, effort and size)and fitting a curve to the data. Future effort estimates are made by providing size and calculating the associated effort using the equation which fit the original data (usually with some error).

Created by Lawrence Putnam, Sr. the Putnam model describes the "time" and "effort" required to finish a software project of specified "size".SLIM (Software LIfecycle Management) is the name given by Putnam to the proprietary suite of tools his company [http://www.qsm.com/ QSM, Inc.] has developed based on his model. It is one of the earliest of these types of models developed, and is among the most widely used. Closely related models areConstructive Cost Model (COCOMO), Parametric Review of Information for Costing and Evaluation – Software (PRICE-S), andSoftware Evaluation and Estimation of Resources – Software Estimating Model (SEER-SEM).

The Software Equation

While managing R&D projects for the Army and later at GE, Putnam noticed software staffing profiles followedthe well-known Rayleigh distribution. [cite web
title = Focus on Lawrence Putnam : A CAI State of the Practice Interview
publisher = Computer Aid, Inc.
date = September, 2006
url = http://www.compaid.com/caiInternet/ezine/larryputnaminterview.pdf
]

Putnam used his observations about productivity levels to derive the software equation::frac {eta cdot Size} {Productivity} = Effort^{1/3} cdot Time^{4/3}

where:
* Size is the product size (whatever size estimate is used by your organization is appropriate). Putnam uses ESLOC (Effective Source Lines of Code) throughout his books.
* The term β is a scaling term and is a function of the project size. [cite web
last = US Government
title = Putnam Special Skills Factor Table
publisher = Data & Analysis Center for Software
date = August 20, 1997
url = https://www.thedacs.com/techs/estimation/comparison.shtml#Table5
]
* Productivity is the Process Productivity, the ability of a particular software organization to produce software of a given size at a particular defect rate.
* Effort is the total effort applied to the project in person-years.
* Time is the total schedule of the project in years.

In practical use, when making an estimate for a software task the software equation is solved for "effort"::Effort = left [ frac {Size} {Productivity} ight] ^3 frac {1}{Time^4}

An estimated software size at project completion and organizational process productivity is used. Plotting "effort" as a function of "time" yields the "Time-Effort Curve". The points along the curve represent the estimated total effort to complete the project at some "time". One of the distinguishing features of the Putnam model is that total effort decreases as the time to complete the project is extended. This is normally represented in other parametric models with a schedule relaxation parameter.

:

This estimating method is fairly sensitive to uncertainty in both "size" and "process productivity". Putnam advocates obtaining process productivity by calibration: :Process Productivity = frac {Size} { left [ frac {Effort}{eta} ight] ^{1/3} cdot Time^{4/3} }

Putnam makes a sharp distinction between 'conventional productivity' : "size" / "effort" and process productivity (Five Core Metrics, pg 97).

One of the key advantages to this model is the simplicity with which it is calibrated. Most software organizations, regardless of maturity level can easily collect "size", "effort" and duration ("time") for past projects. Process Productivity, being exponential in nature is typically converted to a linear "productivity index" an organization can use to track their own changes in productivity and apply in future effort estimates. [cite web
last = US Government
title = Putnam Productivity Parameter Table
publisher = Data & Analysis Center for Software
date = August 20, 1997
url = https://www.thedacs.com/techs/estimation/comparison.shtml#Table4
]

References

See also

*Software estimation

*cite book | last = Putnam
first = Lawrence H.
coauthors = Ware Myers
title = Measures for excellence : reliable software On time, within budget
publisher = Yourdon Press
date = 1991
month = October
isbn = 0-135676-94-0

*cite web
last = Jensen
first = Dr. Randall W.
coauthors = Lawrence H. Putnam Sr. and William Roetzheim
title = Software Estimating Models: Three Viewpoints
publisher = Software Technology Support Center
date = February, 2006
url = http://www.stsc.hill.af.mil/crosstalk/2006/02/0602JensenPutnamRoetzheim.html

*cite web
last = Jones
first = Capers
title = Software Project Management Practices: Failure Versus Success
publisher = Software Technology Support Center
date = October, 2004
url = http://www.stsc.hill.af.mil/crossTalk/2004/10/0410Jones.html

*cite web
last = US Government
title = Modern Empirical Cost and Schedule Estimation Tools
publisher = Data & Analysis Center for Software
date = August 20, 1997
url = https://www.thedacs.com/techs/estimation/toc.shtml

*cite web
last = US Government
title = FAA Pricing Handbook
publisher = Feberal Aviation Administration
date = October, 2005
url = http://fast.faa.gov/pricing/SWpricing.doc

*cite web
last = Sultanoğlu
first = Sencer
coauthors = Ümit Karakaş
title = Cost Estimation Models
date = October 12, 1998
url = http://yunus.hacettepe.edu.tr/~sencer/cocomo.html

*cite web
last = Kemerer
first = Chris F.
title = An Empirical Validation of Software Cost Estimation Models
publisher = Communications of the ACM
date = May, 1987
url = http://www.pitt.edu/~ckemerer/CK%20research%20papers/EmpiricalValidationSwCost_Kemerer87.pdf


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