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Re[2]: RDF vocabulary definitions

From: Leonid Ototsky <leo@mmk.ru>
Date: Thu, 21 Nov 2002 08:42:10 +0500
Message-ID: <5362.021121@mmk.ru>
To: "Richard H. McCullough" <rhm@cdepot.net>
CC: <www-rdf-interest@w3.org>, "David Menendez" <zednenem@psualum.com>

Hello Richard,

Thursday, November 21, 2002, 2:31:44 AM, you wrote:

RHM> 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
RHM> re-finding it later.

RHM> 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
RHM> of types", as you indicated based on your examination of RDF-MT.

The "Class" problem was discussed long time ago in biology etc. It has
much more interesting sides comparing current discussions in the ontology communities !
See for example my paper "To keep abreast of the 21st century" -

Best regards,
mailto:leo@mmk.ru and copy to leo@mgn.ru
Leonid Ototsky,
Chief Specialist of the Computer Center,
Magnitogorsk Iron&Steel Works (MMK)- www.mmk.ru

RHM>   ----- Original Message -----
RHM>   From: Richard H. McCullough
RHM>   To: www-rdf-interest@w3.org ; David Menendez
RHM>   Sent: Wednesday, November 20, 2002 12:29 PM
RHM>   Subject: Re: RDF vocabulary definitions

RHM>   Your excursion into rdf-mt is only obscuring the facts, viz.

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

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

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

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

RHM>     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.

RHM>     As I understand RDF-MT:

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

RHM>     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)),
RHM> ...}

RHM>     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), ...}

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

RHM>     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))

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

RHM>     To summarize:

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

RHM>     eg:Person is a resource of the type rdfs:Class
RHM>     I(eg:Person) is the concept of personhood
RHM>     ICEXT(I(eg:Person)) is the set of resources which are people
RHM> --
RHM> Dave Menendez - zednenem@psualum.com - http://www.eyrie.org/~zednenem/
Received on Thursday, 21 November 2002 00:39:32 UTC

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