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Re: RDF vocabulary definitions

From: Richard H. McCullough <rhm@cdepot.net>
Date: Wed, 20 Nov 2002 12:29:54 -0800
Message-ID: <001301c290d3$96005aa0$bd7ba8c0@rhm8200>
To: <www-rdf-interest@w3.org>, "David Menendez" <zednenem@psualum.com>
Re: RDF vocabulary definitionsYour excursion into rdf-mt is only obscuring the facts, viz.

    Thing, Class, Property are all classes.
    class is an alias of concept.
    RDFS "definition" of class is wrong.
============ 
Dick McCullough 
knowledge := man do identify od existent done
knowledge haspart list of proposition

  ----- Original Message ----- 
  From: David Menendez 
  To: www-rdf-interest@w3.org 
  Sent: Wednesday, November 20, 2002 9:49 AM
  Subject: Re: RDF vocabulary definitions


  At 7:58 AM -0800 2002-11-20, Richard H. McCullough wrote:
    I suppose it would be less confusing to say that
    Property is the class that all properties are subclasses of.
    In the sense used in RDFS, every property is a class.
    For example, hasSex is the class of pairs [person; sex]
    and its individuals are [John Doe; male], [Jane Doe, female], ...


  I think I understand your confusion: you and RDFS are using the word class in different ways.


  An rdfs:Class is a thing which may be used as the value of rdf:type. The set of all members of a rdfs:Class is the set of all resources which have that rdfs:Class as a value of rdf:type.


  As I understand RDF-MT:


  I(X) is the interpretation of the resource identified by X


  IEXT(I(X)) is the extension of a rdf:Property; a set of pairs of the form (subject, object). For example, IEXT(I(eg:hasSex)) = {(I(eg:john_doe), I(eg:male)), (I(eg:jane_doe), I(eg:female)), ...}


  ICEXT(I(X)) is the extension of a rdfs:Class; a set of resources which belong to the rdfs:Class. For example, ICEXT(I(eg:Person)) = {I(eg:john_doe), I(eg:jane_doe), ...}


  ICEXT(X) is defined as the set of Y such that (Y, X) is in IEXT(I(rdf:type)).


  IC is defined as ICEXT(I(rdfs:Class)), the set of resources which represent classes. For all X in IC, ICEXT(X) is a subset of ICEXT(I(rdfs:Resource))


  rdfs:Class and rdf:Property are members of IC. They represent distinct concepts which have different effects on the model.


  To summarize:


  eg:hasSex is a resource of the type rdf:Property
  I(eg:hasSex) is the concept of the property "sex"
  IEXT(I(eg:hasSex)) is the set of pairs corresponding to people and their sex


  eg:Person is a resource of the type rdfs:Class
  I(eg:Person) is the concept of personhood
  ICEXT(I(eg:Person)) is the set of resources which are people
-- 
Dave Menendez - zednenem@psualum.com - http://www.eyrie.org/~zednenem/
Received on Wednesday, 20 November 2002 15:30:01 GMT

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