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Re: namespaces

From: Richard H. McCullough <rhm@pioneerca.com>
Date: Fri, 29 Aug 2008 18:36:37 -0700
Message-ID: <4945F09FD90146CD944CEC504E081FA6@rhm8200>
To: "Richard Newman" <rnewman@twinql.com>
Cc: "Semantic Web at W3C" <semantic-web@w3.org>


You've given me some interesting things to think about.

I have just two brief ideas to follow up with for now.

1. The essence of a "context" is a list of propositions
which disambiguates a particular proposition.  I choose
to talk about namespaces because a)they are lists of
propositions which are already defined for RDF/OWL;
b)the fundamental ones, like rdf and rdfs, are intended
to be the foundation & definition for all other propositions.

2. You seemed disturbed by the idea of time-varying contexts.
They are very natural.  The essence of an action is change --
often with respect to time and space.  So any context which
involves an action -- e.g., walking to the store -- will be time

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 5:20 PM
Subject: Re: namespaces

>> 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 "unambiguous interpretation" is to transform a brief, ambiguous 
> identifier like 'type' into an unambiguous identifier (the full URI) 
> through QName expansion. Namespace declarations are how you tell the  XML 
> parser how to expand the QNames it encounters.
> This is the whole "webby knowledge representation" part -- the use of 
> unique identifiers, rather than the ambiguous terms used by human  beings. 
> No more arguing about whether a lemon is a fruit or a faulty  car. No 
> "fruit flies like a banana, time flies like an arrow".
> The use of QNames is the "much more readable" part, because RDF  becomes 
> very verbose without abbreviations.
> Linked Data does not lose any kind of identification, because the 
> identification you think exists does not exist.
> For example, these three fragments of OWL mean exactly the same thing:
> <?xml version="1.0" ?>
> <rdf:RDF xmlns:owl="http://www.w3.org/2002/07/owl#"
>          xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
>   <owl:Class rdf:about="http://example.org/Foo" />
> </rdf:RDF>
> <?xml version="1.0" encoding="utf-8"?>
> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
>   <rdf:Description rdf:about="http://example.org/Foo">
>     <rdf:type rdf:resource="http://www.w3.org/2002/07/owl#Class"/>
>   </rdf:Description>
> </rdf:RDF>
> <?xml version="1.0" ?>
> <ns0:RDF xmlns:ns1="http://www.w3.org/2002/07/owl#"
>          xmlns:ns0="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
>   <ns1:Class rdf:about="http://example.org/Foo" />
> </ns0:RDF>
> because they all represent the following triple:
>   <http://example.org/Foo> 
> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type
> > <http://www.w3.org/2002/07/owl#Class> .
> The second alternative doesn't include a namespace declaration for  OWL. 
> The third alternative offers different names for the same  namespace 
> declarations. The meaning is the same. Consequently, the  namespace 
> declaration is irrelevant; mere syntactic sugar.
> The N-Triples version doesn't even afford the opportunity to define 
> namespaces, but it has the same meaning in RDF and OWL.
>> The namespaces identify the fundamental definitions that other terms 
>> depend on.
>> If your linked data approach dereferences everything, you lose that 
>> identification.
>> If you don't like the OWL approach, that's fine with me.
> You'll see from my examples above that the namespaces have nothing to  do 
> with identifying the fundamental definitions; the URIs of the  resources 
> do that job.
> In other words, <http://www.w3.org/2002/07/owl#Class> is the  identifier 
> for Class in OWL, regardless of how you syntactically  encode it, or 
> whether a namespace is defined which allows you to  abbreviate it.
> Linked Data says "don't use stupid hacks (like trying to dereference 
> syntax elements such as namespace URIs) to find descriptions of  entities: 
> dereference the entity URIs themselves". You seem to have  latched on to 
> the stupid hack.
>> In the RDF/OWL world, my definition of context is its identification 
>> with an
>> XML namespace.
> You would do better by defining the context as the particular URL from 
> which you fetched a graph -- which only sometimes would be a URL used  for 
> an XML namespace in a particular serialization of the graph.
> Another approach you could take would be to assign contexts to 
> representations fetched by following owl:imports links; these 
> unambiguously refer to other OWL ontologies.
>> 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.
> Any deeper meaning you draw is unfounded. Do not mistake syntactic 
> convenience for formality.
> I advise you to forget about RDF/XML. If it doesn't exist in N- Triples, 
> you should be wary about including it in your mental model of  RDF. RDF is 
> just triples. OWL is built on RDF.
> The one benefit of the many syntaxes for RDF is that they provide  ample 
> opportunities to illustrate that RDF is not defined  syntactically. Stop 
> assigning meaning to syntax. It might be valid in  mKR, but it's not 
> correct to do so in RDF.
> I hope that clarifies things somewhat.
> -R
Received on Saturday, 30 August 2008 01:37:30 UTC

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