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Re: Proposal: variables, templates, and Stickey Cyber Molecules

From: Graham Klyne <GK-lists@ninebynine.org>
Date: Fri, 19 Jan 2001 11:56:04 +0000
Message-Id: <5.0.0.25.2.20010119114602.03f7b5b0@pop3.connectfree.uk.com>
To: Seth Russell <seth@robustai.net>
Cc: RDF-IG <www-rdf-interest@w3.org>
At 07:59 PM 1/18/01 -0800, Seth Russell wrote:
> > I think it is possible to achieve this effect without requiring an explicit
> > indication that the node is a "variable", although I think there is a need
> > to indicate the scope withi which the value/name bindings associated with a
> > node may be applicable.
>
>I responded to this in my last email; but further on you raise some very
>interesting points.
>
> > If one has a node whose URI is unknown, then I propose to just assign it a
> > unique URI.  (I find that leaving the node anonymous is unsatisfactory
> > because one may wish to establish that different occurrences within a
> > context are indeed the same thing.)
>
>This is where I think we need to draw a distinction between internal and 
>external.
>Most implementations assign a unique identifier to any node they create 
>(anonymous
>or not); the question, I think, is whether it is wise to publish that unique
>identifier to the outside world as a URI.  I would weigh in on the side 
>that it is
>not.

Sure.  This is where "scope of applicability", or "context", comes in to 
play.  (It's not necessarily a simple internal/external relationship, 
IMO.)  The URI should still be globally unique, but the assertions about it 
may not be globally reachable/applicable.

> > Then what shall we do when we later discover further information
> > establishing that this resource node, which has by now been bound to a URI,
> > is in fact the same as some other resource in some wider context, which
> > also has a (different) URI.
>
>Well internally if you discover that they should be the same node you just 
>:Smush
>them together and revise all the internal pointers accordingly.  If you 
>haven't
>published a uri for either of them externally then there is no problem 
>whatsoever.

That's too mechanistic an approach for my liking.  Your implementation may 
do this, but it's not how I'd want to model what is going on.

> > One answer is to declare that the two URIs are in fact bound to the same
> > resource.  But this goes against the view held by some that URI:Resource
> > mapping is 1:1-onto.
>
>If you cannot draw a distinction between two nodes, then they should have 
>the same
>internal identifier.  What the outside world does is pretty close 
>to  chaos; but
>when you publish to it, and are consistent, then that helps to simplify 
>the chaos.

I was trying to skirt around this "religious" issue:  some will assert that 
different URIs ipso facto means different resources.  Othersthink that 
multiple URIs can reference the same resource.  (As I've hinted elsewhere, 
I'm trying to muddle along without taking a position;  I think either way 
can work but it would be much easier to discuss the matters if there were a 
widely accepted community consensus on this.)

> > A more flexible approach is to draw on some idea of resource equivalence
> > that allows us to infer properties of one resource from the corresponding
> > properties of another resource with which it is equivalent.  This is the
> > approach I am planning to take in my work.
>
>Hmmm....  this works internally and externally; however it does require that a
>whole slew of equivalences be published along with your statements.  From 
>whence is
>the infrastructure for this kind of thing going to arise?

I don't claim it's a solved problem.  This is one an areas where I'm trying 
to push forward, but resource is spread thin right now so progress is 
slow.  But not non-existent.

#g
Received on Friday, 19 January 2001 08:34:09 GMT

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