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Re: naive question: why prefer absolute URIs to # URIs for linked data?

From: Martin J. Dürst <duerst@it.aoyama.ac.jp>
Date: Mon, 29 Aug 2011 09:51:21 +0900
Message-ID: <4E5AE289.1000409@it.aoyama.ac.jp>
To: Jonathan Rees <jar@creativecommons.org>
CC: www-tag@w3.org, Manu Sporny <msporny@digitalbazaar.com>, Harry Halpin <hhalpin@ibiblio.org>, Ian Davis <me@iandavis.com>
Hello Jonathan,

On 2011/08/29 2:27, Jonathan Rees wrote:
> Question to the broader www-tag readership (and beyond):
>
> I don't want to start another argument, I just want to understand the
> position that it is necessary to use absolute (i.e. hashless) URIs
> instead of hash URIs for semantic web / linked data purposes, and
> record the reasons for this position somewhere. I attempted this in
> http://www.w3.org/2001/tag/awwsw/issue57/20110625/#hash  but I feel
> the case I made against # URIs there is not convincing.
>
> That is, suppose you want a URI to use in RDF as a reference (name,
> "identifier", whatever) for something other than the web page
> (document, "information resource", whatever) at that URI. Why is it so
> important that the URI be absolute, instead of one containing # ?

Just some comment on terminology: While RFC 3986 uses the ABNF 
production <absolute-URI> for an absolute URI without fragment 
identifier, the adjective 'absolute' in connection with 'URI', contrary 
to what your text might suggest, does not imply that there is no '#', 
only that it starts with a scheme and can therefore be resolved 
independent of any 'base' URI.

So while http://www.w3.org/2001/tag/awwsw/issue57/20110625/#hash, for 
example, is not an <absolute-URI>, it is nevertheless an absolute URI 
(because it is independent of the context of a base URI).

For details, please see http://tools.ietf.org/html/rfc3986#section-4.3, 
http://tools.ietf.org/html/rfc3986#section-5.1, and 
http://tools.ietf.org/html/rfc3986#appendix-D.1, where the "without 
fragment identifier" qualification is always present if necessary. That 
the <absolute-URI> production has the name it does seems to come from 
the fact that in a predecessor of RFC 3986, the '#' sign and the 
fragment syntax were treated specially.

Also, as far as I understand, the actual distinction between absolute 
and relative is largely irrelevant for your question; relative URIs 
would just be used for convenience where they are possible because they 
are shorter, but the choice of a relative  (where possible) or an 
absolute URI wouldn't affect the discussion.

So please go through your text and fix occurrences of 'absolute' where 
they are supposed to mean 'hashless'. Just using 'hashless' or 'without 
fragment identifier' should be fine, but if there are cases where you 
have problems with the wording, please feel free to ask for text 
suggestions.

Regards,    Martin.
Received on Monday, 29 August 2011 00:52:15 GMT

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