This specifies the relation between whole and part that should be used for a particular part. For example, the relation between a company and its president may be PresidentOf, PartOf, or whatever the user chooses. The same relation can be used for all the parts, each part can have its own rleation to the whole, or anything in between. For example, a car can have one part-whole relation pointing to all its parts, or it can have one relation for the moving parts and another for the static parts.