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   Re: [xml-dev] URIs and Names on the Web

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>no Semantic Web systems require parsing of a URI in order to draw conclusions about the URI

granted, but in the case of an automated system using the Semantic Web to aggregrate retrievable resources 

about a given subject, is it not necessary to be able to determine if a 
given URI contains some retrievable resource at that location? AFAIK the 
possible solutions at present are:
(1) do a HTTP GET on each URI, and see if you get a response with a MIME 
(2) in RDF, impose some standard means of expressing that the given URI 
is, in fact, a retrievable resource. In Descriptions, it could be a 
distinction between rdf:about (retrievable) and rdf:ID 
(non-retrievable), although thats certainly not part of the standard. It 
could be the use of DC:identifier and DC:format to indicate an URI for a 
retrievable resource and its MIME type.
(3) in XTM, specify a Subject Indicator for retrievable resources and 
their different data format subclasses (HTML, XML, GIF, JPEG etc) and 
use these with topic occurrences. Hopefully, it becomes a Published 
Subject Indicator and is used across topic maps specifying occurrences 
which are retrievable resources.

I question the efficiency of (1), but (2) and (3) only really work if 
the means of specifying the retrievability of a resource can be 
standardized across all the Semantic Web documents that the automated 
system may wish to process during resource aggregration.

Maybe it would have been easier for this scenario if long long ago HTTP 
URIs had been restricted to retrievable resources and other formats used 
for non-retrievable resources. However this would have either 
necessitated URI parsing or in fact the same approach as now, i.e. 
determining an additional property for resources which can indicate the 
type of the resource.

I won't look good for the Semantic Web if intelligent search agents are 
correctly returning URIs relating to the search term but many of these 
URIs don't point anywhere, I suppose at least there should be some 
description (e.g. Dublin Core) applied to non-retrievable URIs so that 
users can retrieve something about search matches.

LJB Nixon


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