What does a merged hierarchy mean and why use one?
Protege ontology means that a class has two or more direct-superclasses. A class may have multiple direct-superclasses however every class must have at least one. The FMA uses single inheritence except in one special case where the META-CLASS hierarchy merges with the THING hierarchy (also termed class hierachy). The results of this merge aids the FMA authors in being very efficient when defining classes, and facilitates fast FMA database queries. To better explain why the authors chose to create this merge I will discuss two possible scenarios. In the first scenario every class that is subsumed by THING can only be a regular class. Every class subsumed by META-CLASS can only be a metaclass (also known as a direct-type). Every regular class must have a metaclass to define the types of own slots it will have. The problem with this scenario is that class information needs to be duplicated to have both metaclasses which define regular classes and the anatomical classes which contain the a
