IsDrivenBy is a reference to provide a relationship from a motor to a drive, which can be a multi-slot-drive or single slot drive. The TypeDefinition of the reference destination as BaseObjectType provides the possibility to point to a slot of a mulit-slot-drive or a motor-integrated-drive. If this reference points to a physical drive (and not a drive slot) it should point to an DriveType.
Annex B.1.9 shows different possibilities of usage.