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Re: Semantic content negotiation (was Re: expectations of vocabulary)

From: Richard Newman <r.newman@reading.ac.uk>
Date: Sat, 29 Jul 2006 22:19:27 -0700
Message-Id: <83C78585-C7F6-4B99-8B44-33D7DFF41321@reading.ac.uk>
Cc: =?ISO-8859-1?Q? "'Reto_Bachmann-Gm=FCr'" ?= <reto@gmuer.ch>, "'Semantic Web'" <semantic-web@w3.org>
To: "Xiaoshu Wang" <wangxiao@musc.edu>

I will step in here to correct a couple of things.

On  29 Jul 2006, at 8:52 PM, Xiaoshu Wang wrote:

>> Sorry, that's nonsense. Not only property URI's are not
>> necessarily dereferenceable and the possibly available graph
>> representation may or may not contain that statement - do you
>> know about any FOAF client behaving as you're suggesting it
>> should? I don't, and I know I wouldn't want to install it on
>> my mobile phone of limited resources.
> Are you sure you are talking RDF? The only thing that is not  
> dereferencable
> is literal values because they are not URI.  But literal can only  
> be an
> object, not subject and property.

Not true. Only a subset of URIs are dereferenceable, and even fewer  
are dereferenceable to yield RDF. The following are a few examples:

- tel:, mailto: etc. URIs
- tag URIs, which are explicitly not dereferenceable
- probably the majority of used HTTP URIs, because they are  
essentially 404s by default, or yield non-RDF data.

Furthermore, not all properties are of the form

<dereferenceable RDF URL> + #propertyName

I often use slashes instead of hashes, and what you get from a web  
server serving up a representation of that URI is probably not a  
fragment of the ontology.

> I don't know too much about FOAF.  But I do know FOAF does not  
> deploy its
> ontology at its namespace (is that why you said a property is not
> necessarily dereferenable?) and I think this practice is a very bad
> practice.  Because it assumes agent to have preexisting knowledge  
> to work
> with something, it sort of make the open-world somewhat closed.   
> IMHO, it is
> bad and very bad.

Last I checked, http://xmlns.com/foaf/0.1/ returns HTML or RDF  
according to your HTTP request, which might be amusing given the  
topic under discussion.

Received on Sunday, 30 July 2006 05:19:39 UTC

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