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Re: Is ontology an information resource?

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 20 Oct 2007 15:56:19 +0200
Message-Id: <D89D6141-33B9-49DB-9A5A-C5020E16F8A5@cyganiak.de>
Cc: semantic-web@w3.org
To: Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>

On 18 Oct 2007, at 16:47, Yoshio Fukushige wrote:
> OK, now that the Classes and properties ARE non-information resources,
> requests for them should be answered with status code 303 (ignoring
> other non-relevant possibilities of codes like, for example, 404).

Yes, assuming that you use slash URIs for your classes and properties.

(You can also use hash URIs, like for example the RDF, RDFS and OWL  
namespaces do. This gives us URIs like http://www.w3.org/2002/07/ 
owl#Class .)

> Then to what URI (IRI) should the Class/property URI be re-directed?
> It is to a URI which dereferences to the defining ontology, right?

You don't *have* to make your class URIs and properties  
dereferenceable, but I think most people would agree that it's a good  
idea and a useful thing to do.

> But should it be the URI of the ontology as a generic (information)  
> resource
> or the URI of one of its representation (specific resource), for  
> example
> RDF/XML file?

I'm not sure what you mean. Representations don't have URIs. And an  
RDF/XML file published on the web *is* an information resource.

Keep in mind that, at the end of the day, “information resource” is  
just a fancy term for “web document”.

Let me give you an example. Here are some classes and properties from  
my ontology:


They all could 303-redirect to this URI:


At this URI, I could serve an RDF/XML representation of the ontology.  
Nevertheless, that URI indeed identifies *the ontology*, an  
information resource, and not a particular representation.

(Again, in a real application I would probably use hash URIs for the  
classes and properties.)

Hope that helps,

> Is there any specification that answers this question?
> If there is none, which is the better practice?
> (I'd be happier with the former, though)
> Many thanks in advance again.
> Best,
> Yoshio Fukushige
> fukushige.yoshio@jp.panasonic.com
> On Mon, 15 Oct 2007 08:06:35 +0200
> Richard Cyganiak <richard@cyganiak.de> wrote:
>> Hi,
>> Short answer: A vocabulary (or ontology) *is* an information  
>> resource.
>> Longer answer: You correctly point out that the documents cited below
>> advocate the use of 303 redirects on vocabulary URIs. However, this
>> has nothing to do with the question wether vocabularies are
>> information resources or not.
>> Note that the 303 status code has existed in HTTP since long before
>> the Semantic Web. A 303 status code simply means: “The server is
>> unable or unwilling to send you a representation of the resource you
>> asked for. Instead, it points you to some related information.” There
>> are many reasons why the server might be unable to provide a
>> representation. One of them is that the resource is not an
>> information resource, but this is not the only possible reason for
>> setting up 303 redirects.
>> But in our case, the reason is a different one. It has to do with
>> content negotiation on hash URIs. (Note that the recipes you cite
>> deal *only* with hash URIs.)
>> According to the specifications, if <myVocabulary> serves HTML, then
>> <myVocabulary#myTerm> identifies a part of that HTML document. If
>> <myVocabulary> also servers RDF via content negotiation, then
>> <myVocabulary#myTerm> identifies whatever the RDF document says, for
>> example a term in my vocabulary.
>> Some people (including me) see this is a contradiction, a URI cannot
>> identify a section of an HTML document and a vocabulary term at the
>> same time. Hence the 303 redirect at <myVocabulary>. It's simply a
>> trick that lets us avoid serving HTML at <myVocabulary>. Instead, we
>> redirect to <myVocabulary.html> and serve the HTML there. This
>> removes the contradiction, <myVocabulary#term> identifies now
>> whatever the RDF says, while the HTML section is identified by
>> <myVocabulary.html#term>.
>> In summary: A 303 redirect does *not* mean that the URI identifies a
>> non-information resource. It just means that the URI *possibly* might
>> identify a non-information resource. In this case, however, it does
>> not. The 303 redirect here is just a trick to avoid a semantic
>> ambiguity arising from content negotiation.
>> Finally, I should point out that W3C's Dan Connolly has gone on
>> record saying that perhaps the ambiguity in this case is not such a
>> big deal, and will possibly be fixed in the future by a simple change
>> to the specifications. So, there's also some precedence for *not*
>> setting up 303 redirects in cases where we have content negotiation
>> on hash URIs.
>> Best,
>> Richard
>> On 15 Oct 2007, at 05:39, Yoshio Fukushige wrote:
>>> Hi all,
>>> I (still again?) have some problems in my attempt to publish an
>>> ontology on the Web.
>>> So please let me solve them by giving your advices.
>>> Let me ask questions one by one, for some of them might be
>>> automatically solved by
>>> preceding answers.
>>> My first question is as follows
>>> QUESTION:  Is an ontology an information resource or non-
>>> information resource?
>>> Reto Bahmann-Gmür said in his message[1] an ontology can be seen as
>>> an information resource, and Tim BL said in his message[2]
>>> [[
>>> when any term in that namespace S looked up, it is the
>>> document <http://ont.example.org/myOnt/example> which is  
>>> dereference.
>>> That resource is the ontology.
>>> ]].
>>> So it seems there is a consensus that an ontology is an information
>>> resource.
>>> In "Best Practice Recipes for Publishing RDF Vocabularies"[3],
>>> however,
>>> Recipe 3, 4, 5 shows
>>> that a Client will receive a 303 response for a request for
>>> 'vocabulary URI',
>>> where the document says in its Introduction
>>> [[
>>> In this document, vocabulary and ontology are used interchangeably.
>>> ]] ,
>>> which together with the TAG's httpRange-14 resolution[4] might imply
>>> that an ontology is a non-information resource...
>>> Chris Bizer's "How to Publish Linked Data in the Web"[5] also  
>>> shows an
>>> example for a client to request a 'vocabulary URI' and get 303
>>> response,
>>> though what 'vocabulary' means is not explicitly defined in that
>>> document.
>>> And Leo Sauermann's 'Cool URIs for the Semantic Web'[6] shows an
>>> example where a request for http://www.acme.com/about#alice (and
>>> http://www.acme.com/about) will get 303 redirect (in section 4.2),
>>> which makes me assume http://www.acme.com/about is a non-information
>>> resource. But is it not an ontology?
>>> Many thanks in advance
>>> [1] http://lists.w3.org/Archives/Public/semantic-web/2007Jul/ 
>>> 0129.html
>>> [2] http://lists.w3.org/Archives/Public/semantic-web/2007Jul/ 
>>> 0132.html
>>> [3] http://www.w3.org/TR/swbp-vocab-pub
>>> [4] http://www.w3.org/2001/tag/issues#httpRange-14
>>> [5] http://sites.wiwiss.fu-berlin.de/suhl/bizer/pub/ 
>>> LinkedDataTutorial
>>> [6] http://www.dfki.uni-kl.de/~sauermann/2006/11/cooluris
>>> Best,
>>> Yoshio Fukushige
>>> -- 
>>> Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>
>>> Network Development Center,
>>> Matsushita Electric Industrial Co., Ltd.
> -- 
> Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>
> Network Development Center,
> Matsushita Electric Industrial Co., Ltd.
Received on Saturday, 20 October 2007 13:56:40 UTC

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