IFPUG function points or COSMIC function points?

Lanza, G.

The choice of the more suitable metric to obtain the functional measure of a software application is not an easy task as it could appear.
Nowadays a software application is often composed by many modules, each of them with its own characteristics, its own programming languages and so on.
In some cases one metric could appear more suitable to measure one particular piece of software than another, so in the process of measuring a whole application it’s possible to apply different metrics: obviously what we can’t do is to add one measure to the other (we can’t add inch with cm!).
In our organization we are starting to use COSMIC function points to measure part of the application and to use IFPUG function points to measure other parts.
One of the possible problem is: “when the management ask us only one measure of the functional dimension of the application what can we do?”
It’s possible to obtain only one measure using the conversion factors from COSMIC to IFPUG but it would be better to maintain two distinct measures.
We are starting to compare the two metrics in different environments: in some cases there is a significant difference in the functional measure.
Using a metric is mainly a matter of culture. It’s important to know what a metric can give us and what not, but above all, what is our goal.
If, for example, our goal is to obtain a prevision of effort and costs we have to know the productivity of each metric in the different environments: so we have to collect data!
This paper illustrates how we can use both the metrics in our application.