Re: Errata Ch 2. Classes - http://www.w3.org/TR/rdf-schema/#ch_classes [SEC=UNCLASSIFIED]

On 16/07/2014, at 3:48 PM, Sam Pinkus wrote:
> 1. Do you really need to state that there is a distinction between a class and its instances? The first paragraph already makes this as clear as it needs to be.
> 
I think so - it isn't as obvious as it might appear (although I don't have that first paragraph with me - perhaps it does cover everything adequately - I shall plough on regardless)

The problem is that normally, (or perhaps philosophically?) "dogs" is simply all dogs. "Integers" is all integers. This isn't problematic because the idea of dogs and actual dogs are - not sure how to express it - on different planes. They have different ontological status. "dogs" lives in the box over there, alongside "Australians" and "things manufactured from wood"; and fido, spot, princess, I and my guitar live in an entirely separate box. 

In RDF, we pull "dogs" down into an object in its own right just like any other object. "dogs" in terms of triples looks exactly the same as "Fido" -  it is an instance of a class, it has a URI, it is a subject and an object of various triples. So at the graph level, it's an object (a URI). At the OWL level, we treat it as being quite different.

When people misunderstand this, it goes like this:

Primus: "but how can a class of things itself be a thing?"
Secundus: "it just is. We have to have *some* way of discussing it"
Primus: "But, if a class is a thing, and all things have a class, the  what's the class of a class?" 
Secundus: "It's the class class, and before you ask, the class of the class class is the class class itself".
Primus: "Wouldn't the class class need a class thats a class class class?" 
Secundus: "No. Why?"
Primus: "It just seems like it should."