PF - Polymorphism Factor

This measure is from the MOOD (Metrics for Object-Oriented Development) suite. It is calculated as a fraction.

The numerator is the sum of overriding methods in all classes. This is the actual number of possible different polymorphic situations. A given message sent to a class can be bound, statically or dynamically, to a named method implementation. The latter can have as many shapes (morphos) as the number of times this same method is overridden in that class's descendants.

The denominator represents the maximum number of possible distinct polymorphic situations for that class as the sum for each class of the number of new methods multiplied by the number of descendants. This maximum would be the case where all new methods defined in each class would be overridden in all of their derived classes.