W3C home > Mailing lists > Public > www-tag@w3.org > June 2006

Re: CURIEs: A proposal

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 27 Jun 2006 12:19:09 -0500
Message-Id: <p06230903c0c714f948f0@[]>
To: "Roy T. Fielding" <fielding@gbiv.com>
Cc: W3C TAG <www-tag@w3.org>

>On Jun 26, 2006, at 8:57 AM, noah_mendelsohn@us.ibm.com wrote:
>>Roy Fielding writes:
>>>All URIs are dereferenceable, not just http URIs -- some
>>>schemes are less amenable to that than others, but there is no
>>>reason to say "http" here.
>>Well, I meant to be silent on the status of non-http schemes.  Clearly
>>there are many other schemes that are typically deferfenceable, and I
>>think I understand the sense in which you mean that all are at least in
>It is an occasional practice for some people to claim that they need a
>new URI scheme because they *do not* want the URI to be dereferenceable.
>That is a common fallacy.  All URI schemes become dereferenceable as soon
>as someone can map any representation associated with the resource to a
>mechanism that accepts a string and returns a representation.

Well, wait a minute. You are saying that any URI scheme *could be* 
dereferenced, given a dereferencing mechanism. Perhaps, but that 
doesn't make the *desire* to have a non-dereferenceable scheme 
fallacious, not does it even mean that there could not be such a 

>  It is just
>harder than using the existing infrastructure for "http" (or "ftp", etc.).
>If you want to be silent on the status of non-http schemes, then don't use
>"http" in the sentence -- the implication is that "http" is somehow
>different in that respect than other schemes.
>>In practice, there is much less deployed infrastructure for
>>dereferencing some other schemes, such as urn, and I didn't want to open
>>that side debate here, which I think might have happened if I had
>>suggested that representations should be deployed for all namespaces,
>>regardless of scheme.  I do agree that it's a good thing to do, not just
>>for http-scheme URIs, but whenever practical.  Turning the argument
>>around, the widespread avaialbility of infrastructure for manipulating
>>http resources is among the reasons for encouraging use of http URIs as
>>names for namespaces.
>That doesn't change the principle that namespace names should be
>dereferenceable *because* Web architectural knowledge should be
>grounded in the Web.

OK, that is a different point, and I think much more debateable. 
There can certainly be non-dereferenceable *naming* schemes. Most 
names are not dereferenceable, in fact. I see no principled reason 
why the Web should be forbidden to use such schemes. In fact, it 
does, although this is not remarked upon in architectural 
discussions, since most of the names in the text on Web pages refer 
in the same way that names in other language texts refer, and this 
mode of reference has nothing to do with dereferencing. Similarly, 
most of the uses of URIreferences in semantic web formalizations are 
at best tangential to this principle, since their intended Web 
functionality has nothing to do with dereferencing, and allowing them 
to be dereferenced has only produced difficulties and controversy, 
and adds nothing to their utility as part of the Web. So there are 
certainly Web names whose Web function has nothing to do with 
dereferencing. It would be a pity if a rational deployment of names 
of this kind were delayed or inhibited by irrelevant 'principles' 
which do not in fact apply to their use on the Web.

>  You have misplaced the principle by trying to
>avoid reference to other schemes.  The principle was intended to cover
>all namespace names, not just those beginning in "http".
>By limiting discussion to "http" namespaces, you are implicitly
>suggesting to people that it is okay to use non-dereferenceable
>namespace names provided that they are not "http" identifiers.
>That is wrong. The principle must be stated in the general case
>even if you happen to be focusing on "http" schemes at the moment.

Why 'must' this 'principle' be stated or even used? Doctrinal 
exhortations which are not supported by empirical or theoretical 
support should always be re-examined critically at regular intervals. 
I am quite unconvinced by this particular 'principle'.

Pat Hayes

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Received on Tuesday, 27 June 2006 17:19:31 UTC

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