Software Cost EstimationFor any new software project, it is necessary to know how much it will cost to develop and how much development time will it take. These estimates are needed before development is initiated, but how is this done? Several estimation procedures have been developed and are having the following attributes in common.
Uses of Cost Estimation
Cost Estimation ModelsA model may be static or dynamic. In a static model, a single variable is taken as a key element for calculating cost and time. In a dynamic model, all variable are interdependent, and there is no basic variable. Static, Single Variable Models: When a model makes use of single variables to calculate desired values such as cost, time, efforts, etc. is said to be a single variable model. The most common equation is: C=aL^{b} Where C = Costs The Software Engineering Laboratory established a model called SEL model, for estimating its software production. This model is an example of the static, single variable model. E=1.4L^{0.93} Where E= Efforts (Person Per Month) Static, Multivariable Models: These models are based on method (1), they depend on several variables describing various aspects of the software development environment. In some model, several variables are needed to describe the software development process, and selected equation combined these variables to give the estimate of time & cost. These models are called multivariable models. WALSTON and FELIX develop the models at IBM provide the following equation gives a relationship between lines of source code and effort: E=5.2L^{0.91} In the same manner duration of development is given byD=4.1L^{0.36} The productivity index uses 29 variables which are found to be highly correlated productivity as follows: Where W_{i} is the weight factor for the i^{th}variable and X_{i}={1,0,+1} the estimator gives X_{i}one of the values 1, 0 or +1 depending on the variable decreases, has no effect or increases the productivity. Example: Compare the WalstonFelix Model with the SEL model on a software development expected to involve 8 personyears of effort.
Solution: The amount of manpower involved = 8PY=96personsmonths (a)Number of lines of source code can be obtained by reversing equation to give: Then L (SEL) = (96/1.4)1⁄0.93=94264 LOC (b)Duration in months can be calculated by means of equation D (SEL) = 4.6 (L) 0.26 (c) Productivity is the lines of code produced per persons/month (year) (d)Average manning is the average number of persons required per month in the project
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