Class hierarchy

All ontologies are structured by using hierarchical class relationships. Moving down the hierarchy leads to more specific classes.

Regional shirt parthas subclassRegion of sleevehas subclassCuff

Moving up the hierarchy leads to more general classes.

Cuffhas superclassRegion of sleevehas superclassRegional shirt part

The superclass relationship is also known as an “is a” (or “is a subclass of”) relationship.

Cuffis aRegion of sleeveis aRegional shirt part

This next example shows the sequence of classes from the most general class in the Shirt Ontology (Physical clothing entity) down to the class Interfacing of collar band:

Physical clothing entityhas subclassMaterial clothing entityhas subclassClothing part
has subclassMaterial of regional clothing parthas subclassMaterial of regional shirt part
has subclassInterfacing of regional shirt parthas subclassInterfacing of region of collar
has subclassInterfacing of collar band

The position of every class within the Shirt Ontology could be traced in a similar way, beginning from Physical clothing entity. (You may be wondering why the most general category in this ontology refers to clothing, instead of a shirt. The ontology has been constructed so that it can be expanded to describe other types of clothing, such as pants. We leave this as an exercise for the reader.)

A shirt has right and left sides. Some parts of the shirt are present in pairs—once on the right side and once on the left side. Classes provide a way to account for this. For example, we can refer to a sleeve in general, or specifically to the right sleeve or the left sleeve.

Regional shirt parthas subclassSleevehas subclassRight sleeve, Left sleeve

In the FMA

The FMA has a very extensive hierarchy of classes. This example shows the sequence of classes from the most general class, called Physical anatomical entity, down to the class Heart:

Physical anatomical entityhas subclassMaterial anatomical entityhas subclass
Anatomical structurehas subclassOrganhas subclassCavitated organhas subclass
Organ with cavitated organ partshas subclassHeart

The FMA also uses classes to account for right and left anatomical structures.

Long bonehas subclassFemurhas subclassRight femur, Left femur