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RE: URN as namespace URI for RDF Schema (run away... run away... ;-)

From: <Patrick.Stickler@nokia.com>
Date: Wed, 6 Oct 2004 15:11:15 +0300
Message-ID: <1E4A0AC134884349A21955574A90A7A50ADD0C@trebe051.ntc.nokia.com>
To: <sandro@w3.org>, <T.Hammond@nature.com>
Cc: <leo@gnowsis.com>, <mdirector@iptc.org>, <www-rdf-interest@w3.org>

> -----Original Message-----
> From: www-rdf-interest-request@w3.org
> [mailto:www-rdf-interest-request@w3.org]On Behalf Of ext Sandro Hawke
> Sent: 06 October, 2004 14:21
> To: Hammond, Tony
> Cc: Stickler Patrick (Nokia-TP-MSW/Tampere); leo@gnowsis.com;
> mdirector@iptc.org; www-rdf-interest@w3.org
> Subject: Re: URN as namespace URI for RDF Schema (run away... run
> away... ;-) 
> > I thought the advantage of using fragments was that (after 
> reconstruction of
> > the original URI from the QName) one would have a natural means of
> > addressing into an XML document (describing the schema) 
> using XPointer
> > methodology. Am I wrong in this?
> I'm afraid you are. While it may be possible to do what you're
> describing, I've never seen it done, and I've never heard the
> advocates of fragment-URIs suggest it.

I perhaps misundertood what Tony was referring to, but I was
taking him to mean e.g. links to "anchor points" (or functional
subcomponents) of documents, such as a section or chapter.

I wasn't actually thinking about how such usage relates to
RDF/XML specifically -- where I agree that noone to date has
demonstrated any trully substantial utility in using URIrefs with
fragment identifiers, i.e. SecondaryURIs (SURIs) to denote 
vocabulary terms rather than URIs without fragment identifiers,
i.e. PrimaryURIs (PURIs); and in fact, in cases of large schemas, 
it has been shown that it is in fact *inefficient* because in order 
to extract some representation of a term denoted by a SURI, one 
must first obtain a (potentially) multi-megabyte representation of 
whatever the base PURI denotes. 

Better to use a PURI to denote the term itself, and be able to
access representations of that term directly without all
the extra overhead.

> The good reasons I've heard are mostly:
>    (1) convenience: dereference of the URI gets the ontology (schema)
>        without any special server configuration

Err... yes, that's the argument, but IMO it's deceptively false 
because it is based on presumptions about schema management practices
which are *known* to not encompass common practice.

You only get the whole ontology, and hence the whole definition
of the term, IFF the entire ontology and all
authoritative knowledge about all terms included therein are
accessible via a single representation, which presumes a single

If the ontology is defined and managed in a modular fashion using 
a number of distinct schemas, then dereferencing the base PURI
of a SURI denoting a term may only result in partial knowledge
about that term, as there may be key knowledge about that term
defined in other schemas/documents/etc.

While such a methodology might work for small ontologies and small 
applications, I think it's been sufficiently demonstrated that such 
an approach does not scale; and the fact that there exist deployed 
systems with ontologies which (a) are defined and managed in a modular 
fashion, and/or (b) already utilize PURIs to denote their terms, it 
is *very* unrealistic, not to mention unreasonable, to presume that 
at this late stage such a methodology could be foisted onto the web 
and semantic web communities as the "right" way to do things.

Also, exactly why would an agent want to always get the
entire ontology (think CYC, Wordnet, etc.) just to find out
what a few *specific* term mean? A parallel would be having to
download an entire mirror of a website to access a single page of
that website after downloading the whole shabang. Yes, for
tiny websites accessible via fast network connections, that
could work, but it certainly wouldn't scale.

>    (2) architectural coherence: some people (notably TimBL) think of
>        non-fragment URIs as identifying documents; they find 
> it jarring
>        (or incoherent) when such URIs are used to identify properties,
>        people, etc.

I would be surprised, and disappointed, if anyone trully found
the idea of using PURIs to denote non-information-bearing resources
either "jarring" or "incoherent". It is true that some folks
employ a (personal) methodology which imposes certain interpretations
and expectations on PURI denoted resources which many other folks
(from what I can tell, a majority of other folks) do not maintain.

But I'm sure that it comes down to preference, and that the more
general view is fully "coherent" to such individuals, even if they
don't much care for it and wish common usage had evolved differently.



>     -- sandro
Received on Wednesday, 6 October 2004 12:11:37 UTC

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