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Re: RDF vocabulary definitions

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Thu, 21 Nov 2002 15:29:56 +0000
Message-Id: <5.1.0.14.0.20021121152436.07a41230@0-mail-1.hpl.hp.com>
To: "Richard H. McCullough" <rhm@cdepot.net>, <www-rdf-interest@w3.org>, "David Menendez" <zednenem@psualum.com>

At 13:31 20/11/2002 -0800, Richard H. McCullough wrote:
>David
>I appreciate your effort.  I'm afraid I was erroneously venting my 
>frustration on you.  I apologize for that.
>
>I have been frustrated in my attempts to pin down the meaning of 
>"Class".  There are so many documents that I have trouble finding one 
>which addresses my concerns, and almost as much trouble re-finding it later.
>
>The first documents that I found when I joined RDF-interest stated 
>(paraphrasing), "Class is concept".  Another document that I found within 
>the last hour stated (paraphrasing) "Class is the set of types", as you 
>indicated based on your examination of RDF-MT.

Richard,

I was thinking that perhaps the schema document might say something more 
about class and did a first rough draft.  Do think including something like 
this in the schema doc would help, or would it just confuse things more?

Brian

RDF Classes

Resources may be divided into groups called classes. The members of an RDF 
Schema class are sometimes known as instances of the class. RDF Schema 
classes are themselves resources. They are often identified by URIref's [@@ 
have we defined the rdf use of this term yet?] and may be described using 
RDF properties. The rdf:type property may be used to state that a resource 
is a member of a class. Two classes may have exactly the same members and 
yet be different classes.

The group of resources that are RDF Schema classes is itself a class called 
rdfs:Class. This may seem a little confusing to some, and especially to 
those who think of an RDF Schema class as a set of resources, for the most 
familiar set theory teaches us that sets cannot be members of themselves. 
However, as explained in [@@RDF-SEMANTICS], a little mathematical trickery 
enables RDF Schema classes to behave like sets whilst still enabling them 
to be members of themselves.

A class A is a subclass of a class B if and only if all the members of A 
are also members of B. All classes are subclasses of themselves. The 
rdfs:subClassOf property may be used to state that one class is a subclass 
of another.

The RDF Concepts and Abstract Syntax [@@RDF-CONCEPTS] specification defines 
the RDF concept of a datatype. RDF Schema defines all datatypes to be 
classes. The members of a class that is a datatype are the members of the 
value space of the datatype.

The core RDF specifications define the following classes.

rdfs:Resource

All things described by RDF are called resources, and are members of the 
class rdfs:Resource. This is the class of everything. All other classes are 
subclasses of this class. [@@ is this true; is it stated or implied in the MT?]

rdfs:Class

This is the class of resources that are RDF Schema classes. rdfs:Class is a 
member of rdfs:Class.

rdfs:Datatype

rdfs:Datatype is the class of datatypes. It is a subclass of rdfs:Class.

....
Received on Thursday, 21 November 2002 10:28:31 GMT

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