Putman’s SLIM (Software LIfe Cycle Management) is an automated ‘macro estimation model’ for software estimation based on the Norden/Rayleigh function. SLIM uses linear programming, statistical simulation, program evaluation and review techniques to derive a software cost estimate. SLIM enables a software cost estimator to perform the following functions:


The SLIM model is based on the Putman’s own analysis of the software life cycle in terms of the Raleigh distribution of project personnel level versus time. The algorithm used is :

K = (size/(CC * t4/3))3

Size is the lines of code, K is the total life-cycle effort (in working years), t is development time ( in years).

C is the technology constant , combining the effect of using tools, languages, methodology and QA procedures etc. The values of the technology constant can vary from as little as 610 up to 57314. Putmans recommended figures for different types of projects are:

  1. Real-Time Embedded 1500
  2. Batch Development 4894
  3. Supported and Organised 10040

In order to use the SLIM model the software size must be identified in advance.

A study carried out by [PENGELLY] indicated that SLIM did not perform accurately on small projects. However, [LONDIEX] reports that SLIM is suitable for software developments that meet the following criteria :

  1. Software size is greater than 5000 lines
  2. Effort greater than 1.5 man years.
  3. Over 6 months development time.

Assessment of SLIM

This page was last updated 12/3/97 Dan. Snell, Bournemouth University, Copyright. 1997