COCOMO MODEL

The Constructive Cost Model (COCOMO) is an algorithmic software cost estimation model developed by Barry Boehm. The model uses a basic regression formula, with parameters that are derived from historical project data and current project characteristics.
COCOMO was first published in 1981 Barry W. Boehm's Book Software engineering economics as a model for estimating effort, cost, and schedule for software projects. It drew on a study of 63 projects at TRW Aerospace where Barry Boehm was Director of Software Research and Technology in 1981. 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.

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 computes software development effort (and cost) as a function of program size. Program size is expressed in estimated thousands of lines of code (KLOC).
COCOMO applies to three classes of software projects:
•    Organic projects - "small" teams with "good" experience working with "less than rigid" requirements
•    Semi-detached projects - "medium" teams with mixed experience working with a mix of rigid and less than rigid requirements
•    Embedded projects - developed within a set of "tight" constraints (hardware, software, operational, ...)
The basic COCOMO equations take the form
Effort Applied = ab(KLOC)bb [ man-months ]
Development Time = cb(Effort Applied)db [months]
People required = Effort Applied / Development Time [count]
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 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.