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Re: Are EPRs identifiers?

From: Mark Baker <distobj@acm.org>
Date: Thu, 9 Dec 2004 22:44:44 -0500
To: Francisco Curbera <curbera@us.ibm.com>
Cc: public-ws-addressing@w3.org
Message-ID: <20041210034444.GS30371@markbaker.ca>

Hi Paco,

On Thu, Dec 09, 2004 at 04:45:42PM -0500, Francisco Curbera wrote:
> Hi Mark,
> 
> It is a pity you missed the discussion we had yesterday at the f2f in
> Redmond.  The case was made (by Jeff M.) that to have identifier semantics
> you need to provide a mechanism that will allow you to decide if two such
> identifiers identify the same entity or not; that is a Boolean valued
> function essentially which will return true or false given a pair of those
> identifiers.

Right.

> This is old news for those familiar with distributed system
> design of course. The spec does not have such a thing because it follows
> the semantics you agreed with below: it allows you to return "true" (in
> fact, only wrt the metadata that applies to the interaction, but let's not
> get into that one now) if you get a byte per byte match of selected fields,
> but you can never get a false answer.

Well, the function will return false if there isn't a "byte per byte
match of selected fields", right?  What I was pointing out in my last
message was that *VERY* few (I couldn't think of any) identification
systems have the property that a syntactic non-match implies a different
thing being identified.  That's just too expensive a proposition in
general.  So I dispute the (apparent) claim that this is a necessary
property of an identification system.

> This is why EPRs do not have
> identifier semantics.

Perhaps it's a terminology problem.  I notice that William Vambenepe,
in the just forwarded pointer to his weblog, said;

"One thing that is clear to me after using EPRs for a while is that they
are not meant to be identifiers, just references."

As I see it, identifiers are references are synonymous.  So do you
believe EPR are references?  If so, what kind of distinction do you draw
between identifiers and references?  Would you call CORBA IORs
identifiers or references?  Would you call a street address an
identifier or a reference?  Would you call an URL an identifier or a
reference?  How about an URN?  And if none of those are identifiers,
what would be an example of one?

I really hope this isn't a can of worms, but it seems important to i001.

Mark.
-- 
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Friday, 10 December 2004 03:42:25 GMT

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