Boehm’s Software Maintenance Model
In 1983, Boehm proposed a model for the maintenance process which was based upon the economic models and principles. Economics model is nothing new thing, economic decisions are a major building block of many processes and Boehm’s thesis was that economics model and principles could not only improve productivity in the maintenance but it also helps to understand the process very well.
Boehm maintenance process model represented as a closed-loop cycle as shown in the below diagram.
He theorizes that it is the platform where management decisions are made that drive the process. In this stage, a set of required changes is determined by applying particular strategies and cost -benefits evaluations to a set of proposed changes. Those approved changes are accompanied by company budgets, which will largely determine the extent and type of resources expanded.
Boehm had understood that the maintenance manager’s task is one of the balancing and the pursuit of the objectives of maintenance against the constraint imposed by the environment in which maintenance work is carried out. That’s why, the maintenance process should be driven by the maintenance manager’s decisions, which are typically based on the balancing of objectives against the constraint. Boehm proposed a formula for calculating the maintenance cost as it is a part of the COCOMO Model. All the collected data from the various projects, the formula was formed in terms of effort.
Boehm used a quantity called Annual Charge Traffic (ACT), which is defined as:
The fraction of a software product’s source instruction which changes during a year either through add, delete or modify.
The ACT is related to the number of change request,
ACT = KLOCadded + KLOCdeleted / KLOCtotal
The annual maintenance effort (AME) in person-months is measured as:
AME = ACT * SDE
ACT = Annual change traffic,
SDE = Software Development effort in person-months.
Annual change traffic (ACT) for a software system is 20% per year. The development effort is 700 PMs. Compute an estimate the annual maintenance effort (AME). If the lifetime of the project is 15 years, what is the total effort of the project ?
The development effort = 700PM
Annual Charge traffic (ACT) = 20%
Total duration for which effort is to be calculated = 15years.
The maintenance effort is a fraction of development effort and that is assumed to be constant.
AME = ACT * SDE = 0.20 * 700 = 140PM
Maintenance effort for 15 years,
= 15 * 140 = 2100PM
So, Total effort,
= 700 + 2100 = 2800PM
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