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RE: article on URIs, is this material that can be used by the SWEO IG?

From: Booth, David (HP Software - Boston) <dbooth@hp.com>
Date: Wed, 30 May 2007 17:09:33 -0400
Message-ID: <EBBD956B8A9002479B0C9CE9FE14A6C202B5B511@tayexc19.americas.cpqcorp.net>
To: "Leo Sauermann" <leo.sauermann@dfki.de>, <www-tag@w3.org>

Although it wasn't requested, :) below is my review of the document

In general, I think this is quite a helpful document.  I had been wanting to find the time to write up something similar myself! :)

Some specific suggestions:

1. Figures 1 and 2 imply that the relationship between the resource URI and the RDF or HTML URIs is direct, but I don't think this is wise, as it prevents one from referring generically to the information resource that describes Alice, which may serve a varying set of content types (determined by content negotiation) that evolves over time.  I think it is better to have the resource URI lead to a related information resource URI that, when dereferenced, serves either HTML or RDF depending on content negotiation.  So in essence the problem (if it is framed the way you have framed it) is essentially about how how to maintain a related *pair* of URIs, such that one is the resource identifier and the other is easily determinable from the resource identifier and is used to retrieve a description of the resource.  

2. It is worth noting that a 303-redirect service such 
as http://thing-described-by.org can also be used:
 - to make it easy to mint 303 URIs without having to do web server configuration; and
 - to enable to extra network dereference that is implied by 303 URIs to be (potentially) optimized away.
See http://thing-described-by.org for more info.

3. There is a third good solution, which involves framing the problem differently.  It is what I called the "shadow ontology" approach: http://lists.w3.org/Archives/Public/public-swbp-wg/2006Jan/0171.html
This approach involves designing your ontology to *indirectly* refer to something that is not a web document, by use of a URI for a web document that describes that thing.   For example:

			<http://example.org/recipies/applePie> .

may indicate that the person who is the primary subject of page http://www.acme.com/people/alice likes to eat the food that is the primary subject of page http://example.org/recipies/applePie .  In essence, the iPreferences:likesToEat property has a range that is "a web document whose primary topic is a person" and its range is "a web document whose primary topic is a food".  In the iPreferences ontology these classes might be called simply iPerson and iFood -- the "i" prefix indicating that they are indirectly identifying a person or food.  Of course, they could just as well be called "Person" and "Food", with the explicit understanding that they indirectly identify a person or food.

In some ways this approach is easier and more straightforward than maintaining related pairs of URIs, but it is only feasible if you control the ontology and can design it accordingly.  

Note that this is different from the "Reference by Description" approach described in section 6.2, because it does not require the extra burden of an additional blank node and inverse functional property.

Note also that this approach can be used very conveniently in conjunction with a 303-redirect service if it later turns out that you want to use your data in conjunction with another oontology like FOAF that already uses foaf:Person to refer to a person directly, such as: 
http://thing-described-by.org?http://www.acme.com/people/alice .

4. Section 6.1 on New URI schemes poses the question: "Shouldn't we create a new URI scheme to identify resources?".  This section should be much clearer that the answer is "No".  The draft TAG finding on "URNs, Namespaces and Registries" 
essentially amounts to a polite, long-winded (but very informative) "no" to this question.  And as my document on "Converting New URI Schemes or URN Sub-Schemes to HTTP" points out:
A simple recipe is presented for converting proposed URI schemes or URN sub-schemes to HTTP using specialized URI prefixes.  . . .  The resulting capabilities of the HTTP URIs are virtually a direct superset of those of URIs based on new URI schemes or URN sub-schemes.

5. Advice 2 in section 3 says: "There should be no confusion between identifiers for documents (URLs) and resource identifiers."  I think you should be a little more careful about your wording there, because document URLs are also a kind of resource identifiers.  I suggest changing the wording to: "There should be no confusion between identifiers for documents (URLs) and identifiers for other things."  Also, note that an "information resource" is not necessarily a document.  It could be a dynamically changing source of representations, such as the current temperature and humidity in Oaxaca.

David Booth, Ph.D.
HP Software
+1 617 629 8881 office  |  dbooth@hp.com

> -----Original Message-----
> From: www-tag-request@w3.org [mailto:www-tag-request@w3.org] 
> On Behalf Of Leo Sauermann
> Sent: Wednesday, May 30, 2007 12:09 PM
> To: www-tag@w3.org
> Subject: article on URIs, is this material that can be used 
> by the SWEO IG?
> Dear TAG,
> The SWEO interest group [3] is searching for tutorial 
> material about the 
> Semantic Web,
> and especially about "URIs in the context of the Semantic Web".
> Richard Cyganiak, Max Völkel and I have written an 
> introductionary article
> "Cool uris for the Semantic Web" [2] summing up the
> TAG-http-range-14 decision [1] and TimBl's favorited "# hash" Uris.
> Now we humbly ask if members of the Tag, could review this 
> article and 
> approve
> its usefulness as tutorial material for people wanting to learn the 
> Semantic Web.
> My question to you is:
> "Can the Article at [2] be used as introductionary material 
> for Semantic 
> Web beginners,
> and can the SWEO interest group circulate it?"
> [Yes]
> [No]
> [Yes, but you have to change ....]
> An Issue that was raised in the semweb-mailinglist and in personal 
> discussions,
> is that we do not mention the possibilities given by using 
> URNs and other
> URI schemes. I argue that this is not necessary for an 
> introductionary 
> article,
> because http URIs are so omnipresent.
> What is your opinion on "having to mention URN and alternative URI 
> schemes is mandatory"?
> regards
> Leo Sauermann
> [1] http://lists.w3.org/Archives/Public/www-tag/2005Jun/0039.html
>      http://www.w3.org/2001/tag/issues.html#httpRange-14
> [2] http://www.dfki.uni-kl.de/~sauermann/2006/11/cooluris/
> [3] http://www.w3.org/2001/sw/sweo/
> -- 
> ____________________________________________________
> DI Leo Sauermann       http://www.dfki.de/~sauermann 
> Deutsches Forschungszentrum fuer 
> Kuenstliche Intelligenz DFKI GmbH
> Trippstadter Strasse 122
> P.O. Box 2080           Fon:   +49 631 20575-116
> D-67663 Kaiserslautern  Fax:   +49 631 20575-102
> Germany                 Mail:  leo.sauermann@dfki.de
> Geschaeftsfuehrung:
> Prof.Dr.Dr.h.c.mult. Wolfgang Wahlster (Vorsitzender)
> Dr. Walter Olthoff
> Vorsitzender des Aufsichtsrats:
> Prof. Dr. h.c. Hans A. Aukes
> Amtsgericht Kaiserslautern, HRB 2313
> ____________________________________________________
Received on Wednesday, 30 May 2007 21:10:33 UTC

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