Base and derived classes

PI Asset Framework (AF) offers a small set of base classes, and a larger set of classes that are derived from the base classes, called derived classes. Derived classes are classes that can be expressed in terms of the UOM base classes. For example, both the Area class and the Volume class are derived from the Length class. You can define virtually all units of measure in terms of a small group of UOM base classes.

PI AF uses the canonical unit for the base class to determine the canonical units for all classes derived from that base class. You cannot change the canonical unit for a base class or a derived class. For example, since the Area class is based on the Length class, the canonical unit for Area is the square meter (m²).

PI AF includes numerous standard UOMs, UOM classes, and conversion factors, but you can always add new ones. It is not typically necessary to create a new base class, although you might occasionally want to add one for non-physical measurements.