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Re: Is ontology an information resource?

From: Richard Cyganiak <richard@cyganiak.de>
Date: Sat, 20 Oct 2007 19:26:34 +0200
Message-Id: <F3FF0119-91F5-4177-A135-96D9E10A5405@cyganiak.de>
Cc: Yoshio Fukushige <fukushige.yoshio@jp.panasonic.com>, SW-forum Web <semantic-web@w3.org>, jarcc Rees <jar@creativecommons.org>, Tim Berners-Lee <timbl@w3.org>
To: Alan Ruttenberg <alanruttenberg@gmail.com>

Alan,

On 20 Oct 2007, at 17:18, Alan Ruttenberg wrote:
>> I'm not sure what you mean. Representations don't have URIs.
>
> This is, at least, confusing. First, we know that there are these  
> "specific resources", which, when we name them, feel a lot like we  
> are naming representations. Second, there are other places that  
> URIs go, such as in Content-location: headers, where it would seem  
> that they in fact do refer to representations.

You are committing a category mistake.

If something isn't a representation *of some resource*, and if it  
isn't generated for the purpose of being *sent in some message* to or  
from that resource, then calling it a representation is entirely  
pointless. Representations are transient things that travel over the  
wire (though they might be stored, cached etc). They are *not* the  
things that are identified by URIs.

You mention the Content-Location HTTP header. It is used to supply  
the URI of a resource that responds reliably with a certain  
representation. At that point, one can gloss over the resource- 
representation distinction and pretend that the URI is the location  
of that particular representation. But one should be aware that one  
is taking a shortcut, at the risk of getting confused.

> After all, resources aren't series of bytes, where representations  
> are. If you make a request for a range of bytes, you must be,  
> therefore, talking about a representation. You can't get a md5 of a  
> resource. You can get a md5 of a representation. At least that's  
> the best I can figure out.

Sure.

>> And an RDF/XML file published on the web *is* an information  
>> resource.
>
> I don't think so. Again, using my best understanding of the  
> terminology, a RDF/XML file is a representation. When we publish it  
> on the web we create a new thing, an information resource, which  
> has this file as one(the only one?)  of its representations.

No, no, no! The web server might read bytes from the file in order to  
generate a representation. Indeed, the process might be as simple as  
taking all bytes from the file and putting them on the wire (plus  
metadata). But that doesn't make the file a representation!

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

Right. Calling certain information resources “documents” is a bit of  
a stretch, e.g. those that respond only to POST.

“Web document” is a useful metaphor that works pretty well for most  
information resources, and hence makes a useful teaching device. It  
is not an engineering term.

Richard


> , though probably one of the roots of the confusion we are all  
> having. Assuming that a web document is a kind of document (that  
> may be an invalid assumption - correct me if I'm wrong) and since  
> documents can't respond to messages, it doesn't make sense to make  
> a POST to a web document, whereas one *can* do a post to an  
> information resource. (or can't I Richard?). Either that, or a POST  
> could never get a 200 response.
>
>> Let me give you an example. Here are some classes and properties  
>> from my ontology:
>>
>> http://example.com/myOntology/myProperty
>> http://example.com/myOntology/myClass
>>
>> They all could 303-redirect to this URI:
>>
>> http://example.com/myOntology.owl
>>
>> 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.)
>
> In a real application I would try to make my server respond more  
> carefully to a request for a class/property than simply pointing to  
> the defining ontology. If the definition ontology is the size of  
> the NCI thesaurus, this is essential if you want to use tools such  
> as tabulator effectively.
>
> Regards,
> Alan
>
>
Received on Saturday, 20 October 2007 17:26:53 GMT

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