Putnam model
Encyclopedia
The Putnam model is an empirical software effort estimation model.
The original paper by Lawrence H. Putnam published in 1978 is seen as pioneering work in the field software process modelling.
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 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 software parametric models
are
Constructive Cost Model (COCOMO
),
Parametric Review of Information for Costing and Evaluation – Software (PRICE-S), and
Software Evaluation and Estimation of Resources – Software Estimating Model (SEER-SEM
).
, Putnam noticed software staffing profiles followed
the well-known Rayleigh distribution.
Putnam used his observations about productivity levels to derive the software equation:
where:
In practical use, when making an estimate for a software task the software equation is solved for effort:
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:
Putnam makes a sharp distinction between 'conventional productivity' : size / effort
and process productivity.
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.
The original paper by Lawrence H. Putnam published in 1978 is seen as pioneering work in the field software process modelling.
As a group, empirical models work by collecting software project data (for example, effort and size)
and fitting a curve
Regression analysis
In statistics, regression analysis includes many techniques for modeling and analyzing several variables, when the focus is on the relationship between a dependent variable and one or more independent variables...
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
Errors and residuals in statistics
In statistics and optimization, statistical errors and residuals are two closely related and easily confused measures of the deviation of a sample from its "theoretical value"...
).
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 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 software parametric models
Software parametric models
A parametric model is a set of related mathematical equations which incorporates variable parameters. A scenario is defined by selecting a value for each parameter...
are
Constructive Cost Model (COCOMO
COCOMO
**********************************************************************************************The Constructive Cost Model is an algorithmic software cost estimation model developed by Barry W. Boehm...
),
Parametric Review of Information for Costing and Evaluation – Software (PRICE-S), and
Software Evaluation and Estimation of Resources – Software Estimating Model (SEER-SEM
SEER-SEM
SEER for Software is an algorithmic project management software application designed specifically to estimate, plan and monitor the effort and resources required for any type of software development and/or maintenance project...
).
The Software Equation
While R&D projects for the Army and later at GEGê
Gê are the people who spoke Ge languages of the northern South American Caribbean coast and Brazil. In Brazil the Gê were found in Rio de Janeiro, Minas Gerais, Bahia, Piaui, Mato Grosso, Goias, Tocantins, Maranhão, and as far south as Paraguay....
, Putnam noticed software staffing profiles followed
the well-known Rayleigh distribution.
Putnam used his observations about productivity levels to derive the software equation:
where:
- Size is the product size (whatever size estimate is used by your organization is appropriate). Putnam uses ESLOC (Effective Source Lines of CodeSource lines of codeSource lines of code 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 source code...
) throughout his books. - B is a scaling factor and is a function of the project size.
- 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:
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:
Putnam makes a sharp distinction between 'conventional productivity' : size / effort
and process productivity.
One of the key advantages to this model is the simplicity with which it is calibrated. Most software organizations, regardless of maturity level
Capability Maturity Model
The Capability Maturity Model is a development model that was created after study of data collected from organizations that contracted with the U.S. Department of Defense, who funded the research. This model became the foundation from which CMU created the Software Engineering Institute...
can easily collect size, effort and duration (time) for past projects. Process Productivity, being exponential
Exponential function
In mathematics, the exponential function is the function ex, where e is the number such that the function ex is its own derivative. The exponential function is used to model a relationship in which a constant change in the independent variable gives the same proportional change In mathematics,...
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.