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Re: comments on http://www.w3.org/TR/2002/WD-rdf-schema-20021112/

From: Richard H. McCullough <rhm@cdepot.net>
Date: Tue, 3 Dec 2002 06:52:06 -0800
Message-ID: <003201c29adb$8d44b200$bd7ba8c0@rhm8200>
To: "Brian McBride" <bwm@hplb.hpl.hp.com>, "Patrick J. Hayes" <phayes@ai.uwf.edu>
Cc: <www-rdf-comments@w3.org>
Brian & Pat
I understand your examples. I think we are in agreement on principles, bit still slightly divergent on terminology.

From my perspective, the post office & tax office are obviously two different contexts -- two different ways of viewing people.  I think in terms of dividing all people into disjoint groups, according to selected properties of the people.  In the first context, the property is defined by the post office; in the second context, the property is defined by the tax office.  The post office - tax office distinction is somewhat clouded by the fact that both properties are measures of physical location.

You'll notice that I said "disjoint groups".  In a given context, overlapping groups constitute an "ambiguous" division.  For example, recall my previous email where Jane Doe belongs to class "man" in Aristotle's context, but belongs to class "woman" in Ms. Feminist's context.

I do not say that a class "is" its members.  I say that a class "denotes" its members, or that the "meaning" of a class is its members, with all their properties.  But that's somewhat beside the point.  The crucial point is that the meaning of a class depends on context.  Context is prior knowledge -- viewed from a particular perspective, possibly characterized as a list of propositions.

Back to the bottom line: defining "Class" in the rdf-schema document.
1. I still say two different classes with the same members imply two different contexts.  
It's your decision how to describe it.
2. I have one other question related to the definition of "Class".  
Is "Person" a subClassOf "Class", and "Dick McCullough" a member/individual of "Class"?  
Or is "Person" a member/individual of "Class", and "Dick McCullough" unrelated to "Class"?
In other words, what is the meaning of "Person"?  And is there a difference between "Resource" and "Class"?
You might add some words to the document to answer this question.
============ 
Dick McCullough 
knowledge := man do identify od existent done
knowledge haspart list of proposition

  ----- Original Message ----- 
  From: Brian McBride 
  To: Richard H. McCullough ; www-rdf-comments@w3.org 
  Sent: Wednesday, November 27, 2002 8:25 AM
  Subject: Re: comments on http://www.w3.org/TR/2002/WD-rdf-schema-20021112/ 


  At 06:02 27/11/2002 -0800, Richard H. McCullough wrote:
  >Yes, I am assuming that two classes with the same members are the same class.
  >
  >If that is not true of rdfs:Class,

  As I wrote before, it is not.

  then either
  >1. you are talking about "currently known members" of a class

  I don't believe that to be the case, as RDF makes no closed world assumptions.

  >or
  >2. you are talking about two "different contexts",

  I don't believe that to be the case either, as we don't define a concept 
  called 'context'.

  >i.e., two different ways of viewing the same individuals,

  Maybe.

  Consider the rdfs:Class A, hypothetically defined by the post office to be 
  the rdfs:Class of people whose address has the same zipcode as mine, and 
  the rdfs:Class B hypothetically defined by the tax office to be the 
  rdfs:Class of people living at the same address as me.  As it happens, 
  classes A and B have the same members.

  A and B have different properties; they are different things.  rdfs:Class A 
  has the property that it is described in a document 
  http://example.org/schema/postoffice, a property that is not true of B. 
  rdfs:Class B has the property that it is described in a document 
  http://example.org/schema/taxoffice, a property that is not true of A.  A 
  and B are different things.  They just happen to have the same members.

  Let me try and bridge the gap here.  There are two different concepts 
  floating around.  I think you call them context and class where a class 
  *is* the set of its members.  Two classes with the exactly the same 
  membership are the identical.  RDFS has a similar but different model.

  In RDFS we have two concepts.  There are rdfs:Class's each of which has an 
  associated set that is the set of its members.  But the rdfs:Class is not 
  the same thing as the set of its members; to use a term I first heard from 
  a colleague that I particularly liked, the set of its members is *nearby*.
  Thats just how it works in RDFS.

  We are not going to get very far if we get your concept of class mixed up 
  with what an rdfs:Class is.

  Now I figure we might take this in steps:

     1.  You need to understand what the RDFS model is, and in doing so, we 
  need to understand from you what bits of the specs are not clear to you.  I 
  think we got the message we should explain the notion of class better :)

     2.  Having figured out what RDFS really is, then you should check it for 
  flaws.

  You should know that we are (I hope) pretty far down the process of writing 
  the spec.  We have decided all our issues and are now just writing them 
  up.  What that means is that for comments of the form:

     o Hey, I've got a better idea; its too late for this round - a future 
  working group will need to look at those.  You have to understand, if we 
  didn't do that we would never get finished.

     o Hey, thats broken because ... we will deal with, though we have to 
  hope there will not be too many of those.

  >with two different sets of relations to other classes.
  >
  >If 1. or 2. is not true, then you're not talking about reality.

  I am writing about RDFS.  Draw your own conclusions.

  Has this helped at all?

  Brian
Received on Tuesday, 3 December 2002 09:52:10 GMT

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