W3C home > Mailing lists > Public > www-tag@w3.org > June 2003

Re: RDDL again

From: Jonathan Borden <jonathan@openhealth.org>
Date: Fri, 13 Jun 2003 10:13:12 -0400
Message-ID: <01f501c331b5$f04b3c90$b6f5d3ce@svhs.local>
To: "Paul Prescod" <paul@prescod.net>, "Tim Bray" <tbray@textuality.com>
Cc: "WWW-Tag" <www-tag@w3.org>

Paul Prescod wrote:
>
> My last message on the topic.

:-)) never say never again. :-))
>
> Tim Bray wrote:
>  > ...
> > I dislike it because it treats nature and purpose asymmetrically.
>

Nature and purpose can be syntactically symmetric (for certain syntaxes) and
semantically asymmetric.

>
> A thing has a nature (which is to say type). A VCR is a VCR.
>
> You are a man. Pretty much everyone would agree. That's just your
> nature. Nature is a property solely of you. On the other hand, purpose
> is a relationship between you and the person "using" you.

agreed.

>
> Your purpose to Antarti.ca is as a founder.
> Your purpose to Lauren is as a husband.
>
> Now consider these assertions:
>
> Tim is a man.
> Tim is a husband.
> Tim is a founder.
> Lauren is a wife.
> Antartica is a company.
>
> The first statement is fine but all of the rest discard important
> information. For all the computer knows, you are the husband of
> Antartica or the founder of Lauren.

Well, not quite, because the computer also knows that Antartica as a company
is not in the class of things that may have a husband, but you can construct
another example that demonstrates the appropriate problem e.g. a group of
friends each of whom is married to _one_ other in the group.

>
> >>  a) of Dan's point that your declarations do not bind appropriately to
> >> the actual resource being described
> >
> >
> > I disagree.  I claim that rfc2396.txt has a nature (.../text/plain) and
> > a purpose (...#normative-reference).
>
> It is a normative reference to some specs and an informative reference
> to other specs. If you don't make the link explicitly then how will it
> get made? Dan raised this earlier and I don't think you answered
> directly. I think that Dan's model makes the purpose type information a
> little harder to find but the other model really discards important
> information.
>
> On the other hand, you are right that RFC2396 is ALWAYS text/plain,
> wherever it is referenced.

RFC2396 need not _always_ be text/plain (e.g. content-negotiation) but
nonetheless RFC2396 is a member of the class of things that has a text/plain
representation.

>
> And by the way, should rddl:nature map to rdf:type? I really don't know
> what rdf:type is for if not to say that "RFC2396" is a "text document"
> or "foo.css" is a "CSS document." When does one use which of
> RDF/RDFS/OWL's various type mechanisms? And when does one invent ones own?
>

I've modelled rddl:nature as rdf:type. This says that "RFC2396 is a member
of the class of things that is a text document". RFC2396 might also be in
the class of things that is an RFC, an HTML document, etc. etc. -- this is
to say that an individual may have any number of rdf:types (the individual
may belong to any number of classes).

RDFS/OWL's 'type mechanisms' are simply class definitions that might allow a
computer to _infer_ that an individual is a member of a particular class,
just as XML Schema's type mechanism might allow a computer to infer that the
string "123" belongs to the class of strings that has an integer
representation.

I'd also say that rddl:purpose can be used to represent an rdf:Property (a
property is attached to an individual).

Jonathan

Jonathan
Received on Friday, 13 June 2003 10:13:27 UTC

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