A common ambiguity occurs when we speak about a pump: is the bare pump meant or the complete pump system with all auxilliaries? In this topic the way to model that is explained.
Like in most cases, a picture tell more than a thousand words:
The impeller and the lube oil system are just 'partOf' examples.
The same applies for a bare turbine vs turbine system.
Creating an ontology
As can be seen it would be possible to create ontologies in the RDL, but that would predictably be subject to too many acceptance problems. But in any RDL extension, that is controlled by some organization other than ISO, it may have success.