[Crm-sig] non-existent objects

[Wolfgang Schmidle]

Dear all,

I am working on Arachne's Cidoc representation, and we came across a 
problem with non-existent objects and how to state their non-existence.

A statue may be set up using e.g. a base or a plinth. In Arachne this 
can be specified in a data field called "Aufstellung" ("setup"). One can 
choose a description from a fixed list, for example "Basisplatte" or 
"Fußplatte/Plinthe". Now, we could model it as

    E22 (the statue, without setup) P46i forms part of E22 (the statue 
plus the setup) P2 has type E55 Type e.g. "Basisplatte"

but I am told that the setup should be seen as a part of the statue. 
Consequently we are modelling it as

    E22 (the statue, including the setup) P46 is composed of E22 (the 
setup) P2 has type E55 Type e.g. "Basisplatte"

However, Aufstellung may also have the value "ohne Basis" ("without 
base"). In this case the second E22 would denote a non-existent object, 
and its Type "ohne Basis" would state the non-existence of this object. 
(If the data field is left empty, we make no statement at all about the 
setup.)

Is this the right way to model it? And is there a problem in RDF with an 
URI for a non-existent object?

Additional question: Does Cidoc have an opinion about the the exact 
meaning of E22 P46 E22 P2 E55 "ohne Basis"? Let's take the word "sheep" 
as an example, where the singular and plural forms are the same: one 
sheep, two sheep. Is it comparable to A) "while most words have a plural 
morpheme, the particular word sheep has none", or B) "for systematic 
reasons we assume that all words have a plural morpheme, but for the 
particular word sheep it is null"?

Thanks,
Wolfgang