Rapid Application Portfolio Sizing

Why is it used?

RAPS is an application of Function Point Analysis (FPA) used to determine a portfolio size in a meaningful and economical way. It can increase an experienced FP analyst's full FPA average counting rate of 500 FP per day to over 5000 FP/day. Most portfolios are larger than 100,000 FP, which could take a man-year without the aid of RAPS.

What is it used for?

The main uses for RAPS are to estimate:

• performance of the Maintenance & Support (M&S) process, both by productivity and defect density
• cost of replacement of all or part of the portfolio
• cost of outsourcing support and maintenance of all or part of the portfolio
• for financial asset valuation purposes.

These methods are not recommended when an accurate FP size is required for example to measure performance on development of a particular system, measuring project productivity, or to add to the body of knowledge for improving estimating.

How does it work?

The first step is to select a representative sample, perhaps 10 - 15% of the portfolio, which is sized accurately (at the 500+ FP/day counting rate) and which is also used to calibrate the chosen FP approximation technique. The selection of the `right' set of sample applications in this first step is critically important for the accuracy of the final size.

In the second step, the remainder of the portfolio is sized using the chosen FP approximation technique - there is a choice of techniques with different balances of speed of counting with accuracy of the end result. In a recent exercise, SMS FP analysts achieved a counting rate of 6000 FP/day, mostly using the most accurate and therefore time-consuming of the approximation techniques.

In the final step, a few of the applications which were sized approximately are re-sized using the fully detailed FP method. This gives a separate check on the accuracy of the sizes obtained by the approximation method.

Benefits of using RAPS

For large portfolios, RAPS provides a meaningful and economical approach to an otherwise near-impossible task.

There can be additional benefits from a RAPS exercise. It forces agreement on what exactly the portfolio comprises - vital if you are in the process of outsourcing - and it will deliver some high-level documentation of the whole portfolio, which otherwise often does not exist.