As defined currently in the spec, DeviceDefinition.parentDevice and DeviceDefinition.hasPart are both referencing a part of a device but in opposite direction (parent and child device type). Shouldn't we avoid representing same concepts in more than one way? I can see the need for having the DeviceDefinition.hasPart element, from which the parent relation can be deducted. I propose to have only one element in DeviceDefinition for representing parts of device. In case we want to keep both, there should be clear reason and better specified definition.