Hierarchical Software Size Metrics

Dozens of different software size metrics have been proposed and used. The most known ones are Lines of Code and Function Point metrics. Former one depicts the physical size and latter the functional size of software. It is known that one metric does not suit for all purposes. For example, Lines of Code may not be a suitable metric for early estimation, and Function Points is a too highlevel metric for some purposes. The most common approach is to use only one metric despite of problems. Another common approach is to use different metrics for different purposes. It is shown here that this approach is not a satisfying one either. There is a need for a hierarchical software size metric that 'grows up' or 'matures' along with software projects. Concerning this kind of metric, the lower levels in the hierarchy can use more detailed information available to decide the values of the metric. We at Nokia Research Center have developed a hierarchical, three-level software sizing metric. It uses the same sizing unit at all levels. The most abstract (the highest) level can be used in early phases andlor for large software projects. The lowest level is detailed enough to bt: used in accurate effort estimation. Hierarchical Software Size Metrics Petri Vesterinen