Generalized Putnam-Parr Software Lifecycle Models

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The software Life Cycle Models due to Putnam and Parr model the software development efforts at almost the extreme ends of the spectrum in terms of difficulty. The Parr model seems to imply that every software effort is a brand new experience and no lessons learned in past experiences can be used beneficially. The Putnam model seems to imply that every software effort is (almost) essentially the same in that there is always some learning involved and that this learning is always linear. In addition, the Putnam model does not take into account the requirements and the feasibility and planning stages of the lifecycle. Parr has objected to this and thinks that all exploratory work pertaining to the project such as 'design studies, requirements analysis or research projects aimed at specific aspects of the task to be attempted' must be accounted for in the model. This paper explores the software development effort with several differential equation models. In these models whether the modeler incorporates the planning and specification stages into the model is left up to the modeler as a 'matter of taste.' Additionally, the 'inherent difficulty' of the software development project is taken into account with the parameters of the models.

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