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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
type
(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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