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Re: Person Identifier

From: Mark Birbeck <mark.birbeck@x-port.net>
Date: Mon, 21 Apr 2008 10:44:19 +0100
Message-ID: <a707f8300804210244j4a8bc63aoae03504639d1216c@mail.gmail.com>
To: "Richard Cyganiak" <richard@cyganiak.de>
Cc: "Bent Rasmussen" <incredibleshrinkingsphere@gmail.com>, semantic-web@w3.org

Hi Richard,

> [...]
>
>  The problem with URNs is that applications need to be modified or rewritten
> before they can know what a URN identifies. That's quite a high cost, and is
> one of the main reasons why many URN schemes never caught on -- not enough
> developers bothered to hardcode support for them into existing applications.
>
>  Naming schemes that piggy-bank on HTTP don't have this problem, HTTP
> support is ubiquitous, and applications can learn that your URI identifies a
> person by making an HTTP request to retrieve a description of the identified
> thing.

I'm afraid this is simply not true, and is actually to turn RDF on its head.

What a URI identifies has nothing to do with the protocol in 'pure'
RDF terms. In the following, my URI identifies a 'FOAF person',
regardless of anything that might be retrieved over HTTP:

  <http://example.org> a foaf:Person .

Now, if these URIs didn't also serve as a means for retrieving
documents, then that would be the end of the story. But of course we
know that it isn't, and that sometimes these URIs also identify
web-pages. Given this fact, you could quite reasonably argue that a
URN is better, because when you use a non-retrievable URI, there is no
ambiguity; i.e., it is simply impossible for a URI to represent both a
person and a web-page if it doesn't begin with "http:".

Which is why I say that getting the type of a resource by making an
HTTP request is to turn RDF on its head. It's to place a particular
problem caused by using one class of URIs (those that begin "http:")
right at the centre of RDF, when RDF itself is completely agnostic
about the detail of resource identifiers.

In my opinion, it's not a great idea to build systems on the basis of
making a web request to check the 'type' of a URI. I think it's far
better to either use some non-HTTP scheme to identify the URI, or to
tack a fragment identifier on the end.

But of course, I understand that people do see the need for such an
architecture, and I also know that this debate will run and run. :)

Regards,

Mark

-- 
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Received on Monday, 21 April 2008 09:44:57 UTC

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