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Re: namespaces

From: Richard H. McCullough <rhm@pioneerca.com>
Date: Fri, 29 Aug 2008 16:22:50 -0700
Message-ID: <3B3A6BF9236C453F805BB6620C940EC5@rhm8200>
To: "Richard Newman" <rnewman@twinql.com>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>

The first several sentences of Section 2.1 are:
Before we can use a set of terms, we need a precise indication of what 
specific vocabularies are being used. A standard initial component of an 
ontology includes a set of XML namespace declarations enclosed in an opening 
rdf:RDF tag. These provide a means to unambiguously interpret identifiers 
and make the rest of the ontology presentation much more readable. A typical 
OWL ontology begins with a namespace declaration similar to the following.

The namespaces identify the fundamental definitions that other terms depend 
If your linked data approach dereferences everything, you lose that 
If you don't like the OWL approach, that's fine with me.

In the RDF/OWL world, my definition of context is its identification with an
XML namespace.

By associating contexts and namespaces, I hope to show the folks on the
Semantic Web list that namespaces are not necessarily mere syntactic
conveniences, that they can have a deeper meaning.

Dick McCullough
Ayn Rand do speak od mKR done;
mKE do enhance od Real Intelligence done;
knowledge := man do identify od existent done;
knowledge haspart proposition list;

----- Original Message ----- 
From: "Richard Newman" <rnewman@twinql.com>
To: "Richard H. McCullough" <rhm@pioneerca.com>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>
Sent: Friday, August 29, 2008 3:44 PM
Subject: Re: namespaces

>> According to section 2.1 of the OWL Web Ontology Language Guide,
>> an ontology begins with namespace declarations.  For example
>>   xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>> I identify "rdf" as the user-friendly name of the context.
>> I identify "http://www.w3.org/1999/02/22-rdf-syntax-ns#" as the URI  of 
>> the context.
>> I identify the propositions contained in the RDF file returned by  this 
>> URI
>> as the propositions which are the context.
> Namespace declarations like that exist to abbreviate (and, in some  cases, 
> make possible) RDF/XML output. They allow you to encode URIs as  QNames.
> Even trivial processing of a chunk of RDF/XML can result in those 
> namespace declarations being stripped away or renamed. Other 
> serializations, such as N-Triples, don't even have namespace 
> declarations.
> The namespaces you are discussing are purely syntactic artifacts.  (Linked 
> Data advocates dereferencing the URI of a resource itself, not  some 
> notional 'namespace'.)
> Consider that:
>  (a) not all URIs are dereferenceable. I could have
>     xmlns:foo="urn:baz" in the document.
>  (b) dereferencing a URI can result in a variety of redirects. A  fetch 
> for that RDF URL could return a 404, or a 302 or 303 to a  different URI. 
> I have no idea what that means in your scheme. How  would you handle 
> redirects and Content-Location headers?
>  (c) the representation retrieved might not be RDF. It is entirely 
> reasonable (in the context of the Web) for the only available 
> representation of the RDF specification to be a PDF, or HTML.
>  (d) in the case of an RDF representation being received, the graph  is 
> not necessarily static.
> All of these are true for resource URIs in general, but especially so  for 
> namespace abbreviations.
> This means you might end up with 'contexts' which cannot be retrieved, 
> have multiple identifiers and friendly names if they can be, and vary 
> over time.
> What do you hope to gain by your assertion? What response are you  looking 
> to receive from this community?
> What is your formal definition of a context in this assertion?
> How is this of interest to the folks on the Semantic Web list?
> -R
Received on Friday, 29 August 2008 23:28:03 UTC

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