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Re: draft-masinter-dated-uri-01.txt

From: Patrick Stickler <patrick.stickler@nokia.com>
Date: Fri, 08 Mar 2002 18:59:30 +0200
To: "ext Williams, Stuart" <skw@hplb.hpl.hp.com>
CC: URI <uri@w3.org>
Message-ID: <B8AEBA92.105A9%patrick.stickler@nokia.com>


On 2002-03-08 18:00, "ext Williams, Stuart" <skw@hplb.hpl.hp.com> wrote:

> Hi Patrick,
> 
> RFC1437 [1] may help with the transfer of a representation of Mary...
> although I suspect that you'd continue to find it contain only a
> representation of a representation of Mary... and not a representation of
> Mary :-)


Good to see the IETF is planning ahead, though...  ;-)


> Stuart Williams
> [1] http://www.ietf.org/rfc/rfc1437.txt
> --
> 
> Date: Fri, 08 Mar 2002 11:07:23 +0200
> From: Patrick Stickler <patrick.stickler@nokia.com>
> To: ext Brian McBride <bwm@hplb.hpl.hp.com>, URI <uri@w3.org>
> Message-ID: <B8AE4BED.103EF%patrick.stickler@nokia.com>
> Subject: Re: draft-masinter-dated-uri-01.txt
> 
> 
> On 2002-03-04 17:22, "ext Brian McBride" <bwm@hplb.hpl.hp.com> wrote:
> 
>> Comments on:
>> 
>>> INTERNET-DRAFT                                         Larry Masinter
>>> draft-masinter-dated-uri-01.txt                         March 1, 2002
>>> Expires September 2002
>>> 
>>>         "duri" and "tdb" URN namespaces based on dated URIs
>> 
>> ... I'm trying to ask whether the two URI's
>> 
>>  urn:duri:2001:http://www.ietf.org
>>  urn:duri:2000:http://www.ietf.org
> 
> My intuitions say that they denote the same resource,
> namely the web location, but at different points in time.
> 
> Thus:
> 
> http://www.ietf.org
>  = A web location
> 
> urn:duri:2000:http://www.ietf.org
>  = The state of http://www.ietf.org at 2000-01-01T00:00:00Z
> 
> urn:duri:2001:http://www.ietf.org
>  = The state of http://www.ietf.org at 2001-01-01T00:00:00Z
> 
> Thus, one could say things that are time dependent about
> the web location named by the URL such as the owner, security
> settings, redirections, etc.
> 
> It doesn't, however, seem to achieve the intended purpose
> of capturing a specific resource residing at that location
> at a given point in time. To do so, one would need a variant
> of the tdb: URI scheme, e.g. tla: "thing located at" and
> use that in conjunction with the duri: scheme. E.g.
> 
> http://www.ietf.org
>  = A web location, where some resource may be accessible.
> 
> urn:tla:http://www.ietf.org
>  = A resource located at http://www.ietf.org
> 
> urn:duri:2000:urn:tla:http://www.ietf.org
>  = The resource located at http://www.ietf.org at 2000-01-01T00:00:00Z
> 
> urn:duri:2001:urn:tla:http://www.ietf.org
>  = The resource located at http://www.ietf.org at 2001-01-01T00:00:00Z
> 
> A URL (sorry for using an obsolete, classical term ;-) is the name of
> a location. That location is itself a resource, and some other non-location
> resource may reside at that location, and one may use the name of the
> location as an indirect alias for the name of the resource residing
> at the location, but the name of the location is not the same as
> the name of the resource accessible from that location.
> 
> Consider the attached RDF/N3 statements, which describe some resources,
> some of which are locations, some of which are resources accessible
> from a named location, and some of which are abstract.
> 
> Note especially that each location resource and non-location resource
> have a diffferent creator and title.
> 
> --
> 
> BTW: I don't see tdb: as being semantically distinct from duri:.
> 
> E.g. in the I-D it is stated:
> 
> "For example, "urn:tdb:2001:http://www.ietf.org" can be used to
>  designate the Internet Engineering Task Force organization, at least
>  as it was described by or referenced by its home page at the first
>  instant of 2001."
> 
> But the 'thing denoted by' the URL http://www.ietf.org is not
> the Internet Engineering Task Force organization, but a web
> location accessible by the HTTP protocol and thus, the above
> tdb: URN is semantically equivalent to the duri: URN
> "urn:duri:2001:http://www.ietf.org", both of which denote the
> state of the web location "http://www.ietf.org" at
> 2001-01-01T00:00:00Z.
> 
> If one wishes to denote the Internet Engineering Task Force
> organization itself, then they should use a non-location specific
> URI to do so, such as a voc: URT or similar non-dereferencable
> name, or some anonymous resource; e.g.:
> 
>  [ a x:Organization ;
>    x:name "Internet Engineering Task Force" ;
>    x:homePage <http://www.ietf.org> ]
> 
> There is no need for any tdb: URI scheme, because the 'thing
> denoted by' a URI is the thing denoted by the URI, nothing else.
> 
> A URI does not denote two things.
> 
>> Is it possible to argue that:
>> 
>>  http://mycollege.edu/students/Mary
>> 
>> does indeed name Mary, and what you get when you do an HTTP GET
>> on that URL is a representation of Mary?
> 
> Well, aside from Star Trek technology, I don't see how you would
> GET a representation of Mary, per the semantics of HTTP. You might
> GET a representation of Mary's home page, or of her CV, or of a photo
> of Mary, etc. but you wouldn't GET a representation of *Mary* herself.
> 
> To some extent, the use of the term 'representation' by HTTP is
> unfortunate, because in non-HTTP terms, a photo is a representation of
> Mary -- but in the HTTP world, there is an additional level
> of indirection between the non-HTTP representation of Mary (the photo)
> and the HTTP representation of the non-HTTP representation of
> Mary (the byte stream returned by GET), and these two levels of
> indirection often get confused such that folks think that what is
> returned by GET is a representation of Mary herself, rather than
> the actual case, which is that what is returned is a representation
> of the representation of Mary. (ouch, my head hurts... ;-)
> 
>> Leaving aside, however sorting out what the properties of resources are,
>> I wouldn't write the RDF example above that way, as it is at best,
>> likely to confuse.  Better would be:
>> 
>> <rdf:RDF>
>>  <rdf:Description about="http://mycollege.edu/courses/6.001">
>>    <s:students>
>>      <rdf:Bag>
>>        <rdf:li rdf:parseType="Resource">
>>          <foo:homepage resource="http://mycollege.edu/students/Amy"/>
>>        </rdf:li>
>>        <rdf:li rdf:parseType="Resource">
>>          <foo:homepage resource="http://mycollege.edu/students/Tim"/>
>>        </rdf:li>
>>        <rdf:li rdf:parseType="Resource">
>>          <foo:homepage resource="http://mycollege.edu/students/Mary"/>
>>        </rdf:li>
>>      </rdf:Bag>
>>    </s:students>
>>  </rdf:Description>
>> </rdf:RDF>
>> 
>> which inserts extra resources to 'represent' the students as different
>> resources from their home pages.
> 
> Yup. Exactly.
> 
> The students are not their home pages.
> 
> Cheers,
> 
> Patrick
> 
> --
>              
> Patrick Stickler              Phone: +358 50 483 9453
> Senior Research Scientist     Fax:   +358 7180 35409
> Nokia Research Center         Email: patrick.stickler@nokia.com
> 

--
               
Patrick Stickler              Phone: +358 50 483 9453
Senior Research Scientist     Fax:   +358 7180 35409
Nokia Research Center         Email: patrick.stickler@nokia.com
Received on Friday, 8 March 2002 14:44:32 UTC

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