Questions on FOAF design?

Hi:

I
was reading through the FOAF (N3 serialization), as a good example to
use some of the design decisions there, to help in the design of our
own ontology. I had some questions in the process and was hoping folks
on this list could throw some light. These are not criticisms,
obviously, but genuine queries of someone new to the intricacies of
ontology design...

In FOAF:


1. Why are (re)defining
terms, e.g. wot:assurance to be an owl:AnnotationProperty. It is
already defined as an owl:ObjectProperty in the WOT ontology --
shouldn't we defer to that source ontology instead of defining our own,
especially when AnnotationProperty and ObjectProperty are meant to be
disjoint. How is this being used?

2. Why do we have to define here what rdfs:Class, as in rdfs:Class is an owl:Class is? Shouldn't that be available to a reasoner from the RDFS ontology?

3.
I see combinations of camel casing and underscore and other schemes 
for naming resources, properties with conjuctions of more than one word
-- even for the terms FOAF defines itself. e.g. based_near and
firstName. Wouldn't consistent naming have been better?

4. What
is the way to modify/adapt (subtle or not not subtle) the semantics of
a term / property -- example I don't want foaf:interest to be a
"document", as in, foaf:Document. I may want it to be just a list of
"terms" or concepts, or maybe "interest" in my application domain is
not a document, but much broader, say owl:Thing, or whatever...  Do I
define my own property, how do I "extend" foaf:interest ? In general
what are the semantics of "is-a"; are they as strict as in OO type
inheritance, where EVERYTHING TRUE about the super class must also
atleast hold true about the subclass? I've seen IS-A used "loosely" in
several RDFS/OWL documents. In FOAF for instance, many wide "wordnet
concepts" are said to parents of foaf properties, but those wordnet
concepts are open to wide interpretation, fuzzy semantics, and I'm not
sure how we can definitively say, my class IS-A particular wordnet
concept. What's an organizing principle in situations such as these?


Regards,
Revi