W3C home > Mailing lists > Public > xml-uri@w3.org > May 2000

Re: Web Architecture, 'XML Autonomy'

From: Rick JELLIFFE <ricko@geotempo.com>
Date: Thu, 25 May 2000 00:16:35 +0800
Message-ID: <392C0063.739A918F@geotempo.com>
To: xml-uri@w3.org
 
> Based on this discussion and outliers to it, I'd strongly suggest that the
> W3C step back for a while to clarify both their basic architecture and the
> approach to achieving it.  Alternatively, I'd suggest that clarification of
> the relatively simple layering issue - what is the role of XML in the
> semantic Web? - might be enough to get this wagon out of the mud.
 
Tim BL makes interesting statements in
http://www.w3.org/DesignIssues/Meaning.html
When I first read them, I thought he was just being loose (since the
documents are
just sketched out) but in fact it seems he is being exact.

"In XML, a language is a "namespace", and the document about the
language is called a "schema". 
In XML, one document can contain a mixture of languages, and so the
schema if written in XML may contain information about syntactic
constraints (in XML-schema language) 
and/or RDF properties (in rdf-schema language), or any combination of
the above. (note)
               
"XML puts no contraints on a language apart from syntactic structure.
There is not (without RDF 
and logic or some other higher level) any overall framework into which
new languages can be introduced. So, the question of what an XML
document means depends 
first upon the fully qualified name of the document element. No
semantics
can be attached to any of its descendents in the document tree except in
as much as is 
defined by the specification of that element type in that namespace. One
cannot talk
about the "meaning" of a subtree of a document without understanding the 
semantics of the language. In fact, because languages only necessarily
define meaning for
documents, the only way one can talk about the meaning of a subset of a
document is 
to define a how those parts of the document can be reassembled into a
second whole
document. This is what must be done when a digital signature is applied
to a document. "

 

According to this vision:

 * a language = namespace  (therefore derefencing a namespace URI should
yield a language definition, I suppose)
 * the document element ultimately determines semantics of subelements  
 * semantics are only determined by element name and namespace name, in
context.

I cannot imagine that this vision is shared by many people: the more
common position would perhaps be

 * a vocabulary = namespace 
 * any information item can contribute to the semantics of any other
information, whether in the same branch or not
 * semantics can be determined by many other factors including position,
presence or absense of attributes, etc. 


XML Schemas seems to be neutral to both views, I think.

Rick Jelliffe
Received on Wednesday, 24 May 2000 12:08:22 UTC

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