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Re: i0001: EPRs as identifiers - alternative proposal

From: Francisco Curbera <curbera@us.ibm.com>
Date: Thu, 2 Dec 2004 12:33:43 -0500
To: "Mark Peel" <mpeel@novell.com>
Cc: public-ws-addressing@w3.org
Message-ID: <OF05D98087.A5E23915-ON85256F5E.005FE518-85256F5E.00607845@us.ibm.com>

Mark,

Even for the hosting system, it is different to say that the EPR is the
identifier from saying that it can be used to find out the identifier. I
can have many EPRs for the same resource and to check for identity I lookup
the actual identifier corresponding to each EPR and then check for
equality. That does not make the EPR into an identifier.

On the other hand, what the hosting system does internally is not
necessarily our focus, just a source of important requirements. The
interoperable side of it is what we need to focus on; that is the only
perspective that clients (should) have. If we tell them that EPRs can be
used as identifiers we are going to get them in trouble sooner or later.

Paco




                                                                                                                                        
                      "Mark Peel"                                                                                                       
                      <mpeel@novell.com        To:       Francisco Curbera/Watson/IBM@IBMUS                                             
                      >                        cc:       <public-ws-addressing@w3.org>                                                  
                                               Subject:  Re: i0001: EPRs as identifiers - alternative proposal                          
                      12/02/2004 11:50                                                                                                  
                      AM                                                                                                                
                                                                                                                                        





  Could someone please explain the context in which it matters if an
EPR is an identifier?  It seems an EPR identifies little to a client
system, which cannot compare 2 EPRs with much hope of determining
whether or not they refer to the same web service.  At the same time, an
EPR *perfectly* identifies a web service to the system that hosts it: we
don't send SOAP messages to http://someserver.somehost.com/occupant and
hope that a web service on the target system will respond to our
request.  It seems to me that answering "who wants to use the EPR as an
identifier?" would clarify this issue.

Best wishes,

Mark Peel
Web Services Infrastructure
Novell, Inc.

>>> Francisco Curbera <curbera@us.ibm.com> 12/02/04 10:08 AM >>>

Mark,

I think that the argument (in your referenced mail below) that
addresses
are some form of identifiers is rather weak. Alternatively, it is a
strong
argument claiming that addresses are very weak identifiers :-)
Architecting
systems on the assumption that you may identify resources with an
address
is a recipe for disaster. The idea that network endpoints can be
provided
URI identifiers is a different matter; my opinion is only that runtime
service endpoint addresses should not be constrained to be URIs
(although
some may want to do just that).

Paco





                      Mark Baker

                      <distobj@acm.org>               To:
Francisco Curbera/Watson/IBM@IBMUS

                      Sent by:                        cc:
public-ws-addressing@w3.org

                      public-ws-addressing-req        Subject:  Re:
i0001: EPRs as identifiers - alternative proposal

                      uest@w3.org





                      12/02/2004 12:05 AM








Hey,

On Wed, Dec 01, 2004 at 01:00:27PM -0500, Francisco Curbera wrote:
> Rationale
> =======
>
> EPRs are not identifiers, only addresses. Let me explain.

FWIW, after the RefProps/RefParams discussion, I now agree that EPRs
are not necessarily identifiers.  But I don't see them as addresses
either, since addresses are identifiers[1].

IMO, the best way to think of this is with the EPR as a 2-tuple with
an
identifier and some contextual state, in exactly the same way we think
of http URIs and cookies.  So, I believe that an EPR is an identifier
iff it contains no contextual state, i.e. no RefParams.

> One remaining question is whether EPR (as addresses) should be URIs
but I
> think this should be opened as a separate issue.

I disagree.  I think it's part and parcel.  But no biggie, as long as
it
gets its day in court. 8-)

So unfortunately, I'm -1 on the proposal.  And I'd consider writing up
my own proposal, but it involves removing RefProps (to provide a
single
identifying data element), and I don't see that flying just yet.  But
we'll see where DavidB and Hugo get on that front ...

 [1]
http://lists.w3.org/Archives/Public/public-ws-addressing/2004Nov/0588.html


Mark.
--
Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
Received on Thursday, 2 December 2004 17:34:19 GMT

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