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Re: Another fragment issue

From: Sean B. Palmer <sean@mysterylights.com>
Date: Fri, 18 May 2001 15:58:23 +0100
Message-ID: <02bc01c0dfab$1c6d4a20$17d993c3@z5n9x1>
To: "Pierre-Antoine CHAMPIN" <champin@bat710.univ-lyon1.fr>, "Aaron Swartz" <aswartz@swartzfam.com>
Cc: "RDF Interest" <www-rdf-interest@w3.org>
> Some document in DI claims that there is no fundamental
> difference btw URIs and URI refs. [...]

Hmm... maybe you're reading a totally different set of TimBL's
DesignIssues to me. How could there be no fundamental difference
between URIs and URI refs? The complication (annoyance) is that in
RDF, a "resource" can be identified by a URI or a URI-Ref, whereas in
the URI RFC, a resource is what's identified by a URI, and a URI-Ref
is a "view" of that resource. It was a bit foolish to reuse the same
word for a different concept.

Still, according to TimBL (as far as I can tell from DesignIssues) in
HTTP, a URI identifies some material "suitable for HyperText
transfer", but not some kind of generic concept. Some people disagree
with this (Sandro?), stating that "the homepage of Dan" can also be
used to represent Dan himself, as long as the two aren't muddled...
but it's murky ground.

Anyway, I think that the following is quite explicit:-

It is important, on the Semantic Web, to be clear about what is
identified. An http: URI (without fragment identifier) necessarily
identifies a generic document. This is because the HTTP server
response about a URI can deleiver a rendition of (or location of, or
apologies for) a document which is identified by the URI requested. A
client which understands the http: protocol can immediately conclude
that the fragementid-less URI is a generic document. This is true even
if the publisher (owner of the DNS name) has decided not to run a
server. Even if it just records the fact that the document is not
available online, still a client knows it refers to a document. This
means that identifiers for arbitrary RDF concepts should have fragment
identifiers. This in term means that RDF namespaces should end with
]]] - http://www.w3.org/DesignIssues/Fragment

Because "resources" in RDF covers URI-Refs as well, I normally use
namespaces with a "#" on the end just to be safe. It's easier for
maintainance purposes that way as well (although not always).

Kindest Regards,
Sean B. Palmer
@prefix : <http://webns.net/roughterms/> .
:Sean :hasHomepage <http://purl.org/net/sbp/> .
Received on Friday, 18 May 2001 11:47:54 GMT

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