How does ORM compare to RDF and OWL ?
Terry discusses this in the BBB pages 865-871.
Here are some edited extracts:
RDF identifies resources by a URI reference. (ORM identifies object entity types using an identifier)
RDF allows you to state that a class is an instance of itself and so is exposed to logical problems such as Russell's paradox.
OWL does not have a graphic notation. Thus, fact types and their restrictions are declared textually. (Which for me makes it much more verbose)
OWL uses the "open world assumption" . This means that failure to find or to infer some proposition does not imply that the proposition is false.
So it seems to me that OWL is exposed to the logical equivalent of "nulls" which means that in OWL, the answer to the question "Is this proposition true or false" could be either Yes, No or Maybe. (Not very good for logical analyses!)
ORM has the notion of an "atomic fact" which simply put, is an assertion that cannot be expressed in a simpler form without loosing information.
In practice, one sometimes encounters atomic facts which can only be expressed using a ternary, a quaternary or an even higher "n-ary" fact.
Thus, ORM supports the use of n-ary fact types.
ORM's n-ary fact types can be mapped to binary fact types but with potential loss of information. For example some ORM constraints and derivation rules have no counterpart in the description logics on which RDF and OWL are based.
RDF and OWL are restricted to binary fact types. Thus they are less expressive than ORM.
There are presentations in the ORM Events section of the Library that discuss aspects of your question.
Most of the presentations are based on papers that have been published in Springer-Verlag's Lecture Notes on Computer Science.
Where a paper exists, it is referenced in the description of the presentation.
Hope this helps