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draft-masinter-dated-uri-01.txt

From: Brian McBride <bwm@hplb.hpl.hp.com>
Date: Mon, 04 Mar 2002 15:22:31 +0000
Message-Id: <5.1.0.14.0.20020304133917.04eb3d30@0-mail-1.hpl.hp.com>
To: uri@w3.org
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

[...]

>1.1 Intrinsically Persistent Identifiers
>
>Many people have wondered about how to create globally unique and
>persistent identifiers. There are a number of URI schemes and URN
>namespaces already registered. However, many of them lack an adequate
>guarantee of both uniqueness and persistence.

We stray into murky waters here.  What is meant by persistence?
How can a persistent URI be distinguished from a non-persistent one?

[...]


>    * permanent (the identity of the resource identified
>        is not subject to reinterpretation over time)

Interesting choice of words.  What is an interpretation of the
identity of a resource?  How can one tell whether the identity
of a resource has been 'reinterpreted'.

[...]

Can we make this a little clearer.

Let's assume for the purposes of argument, that I did an http get
on http://www.ietf.org at the first instant of the year 2000 and
the first instant of the year 2001, that no error occurred and that
the sequence of characters returned was not the same on the two
occasions.

Is it true that any time invariant property of

   urn:duri:2001:http://www.ietf.org

is also a time invariant property of

   urn:duri:2000:http://www.ietf.org

The two dates are intentionally different.

e.g. if the creation date of:

   urn:duri:2001:http://www.ietf.org

is D, then is the creation date of

   urn:duri:2000:http://www.ietf.org

also D. I don't mean logical entailment for any URI here, I'm
asking specifically about http://www.ietf.org.

Assuming its the resource not the respresentation that

   urn:duri:2001:http://www.ietf.org

names, then, I'm trying to ask whether the two URI's

   urn:duri:2001:http://www.ietf.org
   urn:duri:2000:http://www.ietf.org

name the same resource.

[...]


>The relations in RDF, however, may already provide for the "thing
>described by" indirection. For example, the example in Section 3.2.1
>of [RDF] claims the model for the sentence
>
>            "The students in course 6.001 are Amy, Tim and Mary"
>
>would be written in RDF/XML as
>
>  <rdf:RDF>
>    <rdf:Description about="http://mycollege.edu/courses/6.001">
>      <s:students>
>        <rdf:Bag>
>         <rdf:li resource="http://mycollege.edu/students/Amy"/>
>         <rdf:li resource="http://mycollege.edu/students/Tim"/>
>         <rdf:li resource="http://mycollege.edu/students/Mary"/>
>       </rdf:Bag>
>     </s:students>
>   </rdf:Description>
></rdf:RDF>
>
>but the resources listed are web pages (served by HTTP) and the class
>and students are the "things described by" those web pages.

This gets into more muddy water because the core of web architecture
isn't very well defined.

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?

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.

Thus RDF does not need tbd; it has enough machinery to
handle the indirection required.  Were there other applications you had
in mind?

Brian
Received on Monday, 4 March 2002 10:25:07 UTC

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