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Re: i0001: EPRs as identifiers

From: David Booth <dbooth@w3.org>
Date: Wed, 17 Nov 2004 02:30:53 -0500
To: public-ws-addressing@w3.org
Cc: Francisco Curbera <curbera@us.ibm.com>, Savas Parastatidis <Savas.Parastatidis@newcastle.ac.uk>
Message-Id: <1100676653.3580.926.camel@nc6000.w3.org>

Paco & Savas,

Regarding:
http://lists.w3.org/Archives/Public/public-ws-addressing/2004Nov/0355.html
http://lists.w3.org/Archives/Public/public-ws-addressing/2004Nov/0358.html

If I understand you correctly, you are arguing that an EPR is *not* used
to identify "the service", rather it is merely used to route messages to
one of several delivery points belonging to the same logical "service".

While I think it's reasonable to view a collection of delivery points as
belonging to the same logical "service", the issue is that these other
delivery points are *also* interesting resources, and thus deserve their
own URIs, as the WebArch explains[1].  In other words, there are several
interesting resources -- one of them being the thing that you consider
"the service" -- and they are related to each other.

Even if we were to assume that the word "identify" is misleading (and
therefore ignore it), both the WS-Addressing specification and Gudge's
presentation make it quite clear that RefProps are used to identify
other resources.

Gudge's presentation states:
http://www.w3.org/2002/ws/addr/4/10/img5.html
[[
Endpoing addresses are made up of two pieces:
 - An address
 - A sub-address
]]
Whatever is being addressed by the combination of the address and
sub-address sure sounds to me like a distinct resource -- whether or not
you choose to call it a different "service".

Gudge's presentation also states:
http://www.w3.org/2002/ws/addr/4/10/img13.html
[[
Different Reference Properties imply different metadata
e.g., different wsdl:binding, policy
]]
If something has different metadata, it sure sounds to me like a
different resource.

WS-Addressing spec Sec 2.1
http://www.w3.org/Submission/2004/SUBM-ws-addressing-20040810/#_Toc77464318
[[
Consuming applications SHOULD assume that endpoints represented by
endpoint references with different [reference properties] may accept
different sets of messages or follow a different set of policies, and
consequently may have different associated metadata (WSDL, XML Schema,
and WS-Policy policies ).
]]
Again, if they accept different sets of messages and have different
WSDL, they sure sound to me like different resources.

WS-Addressing spec Sec 2.4
http://www.w3.org/Submission/2004/SUBM-ws-addressing-20040810/#_Toc77464321
[[
a consuming application should assume that different XML Schemas, WSDL
definitions and policies apply to endpoint references whose address or
reference properties differ.
]]
Again, these sound to me like distinct resources, whether or not you
choose to call them different "services".

Even if you personally would not consider the resource that is
identified by distinct RefProps to be a different "service", many people
would, given that it may be described by a different WSDL document and
thus may even have an entirely different interface.

Reference
1. WebArch, Good practice on the use of URIs:
http://www.w3.org/TR/2004/PR-webarch-20041105/#pr-use-uris

-- 

David Booth
W3C Fellow / Hewlett-Packard
Received on Wednesday, 17 November 2004 07:30:54 GMT

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