RE: abstract class

>   thing in all objects that can have color, all them
> will have the property color, then the domain of the
> property color is going to be ObjectsWithColor, but we
> don't want objects that are type of ObjectsWithColor
> ant not type of anything else.

Again I think you are confusing "Class" in OO with "Class" in RDF.

<x> <rdf:type> <ObjectsWithColor> doesn't mean that <x> is not of any type
other than <ObjectsWithColor>. It is perfectly okay to have that statement
on its own.

Similarly in you're earlier example <#foo> <rdf:type> <A> entails the
statement <#foo> <rdf:type> <C>.

Indeed it for any resource #bar one can accurately, if needlessly compose
the RDF/XML:

<rdfs:Resource id="#bar"/>, and that's a superclass even of your <C> class.

This isn't a programming language. It is a language for describing
resources.

Compare with English. When I say "I am a human being", that statement isn't
untrue because I didn't use the more accurate "I am a man" or "I am an
Irishman" or "I am a married Irish Software Developer between the ages of 25
to 35 in full-time employment who is registered to vote and doesn't drive a
car".

Classes in RDF are far more comparable to nouns in English than to classes
in OO.