- From: Francisco Curbera <curbera@us.ibm.com>
- Date: Sat, 6 Nov 2004 23:27:56 -0500
- To: "Vinoski, Stephen" <Steve.Vinoski@iona.com>
- Cc: "David Orchard" <dorchard@bea.com>, "Newcomer, Eric" <Eric.Newcomer@iona.com>, "Martin Gudgin" <mgudgin@microsoft.com>, public-ws-addressing@w3.org, public-ws-addressing-request@w3.org, "Bergersen, Rebecca" <Rebecca.Bergersen@iona.com>
- Message-ID: <OF30BAA975.0E04AB25-ON85256F45.0017E3E5-85256F45.001886BF@us.ibm.com>
One possible approach is to architect embedded metadata into the EPR that
allows encoding alternative addresses for each protocol - somehow using the
address field as a logical address in this case. This is a possible use
case of the embedded metadata I was asked to rationalize and a possible
alternative for this issue. Comments?
Paco
"Vinoski, Stephen"
<Steve.Vinoski@iona.com> To: "David Orchard" <dorchard@bea.com>, "Martin Gudgin" <mgudgin@microsoft.com>,
Sent by: "Bergersen, Rebecca" <Rebecca.Bergersen@iona.com>, <public-ws-addressing@w3.org>
public-ws-addressing-req cc: "Newcomer, Eric" <Eric.Newcomer@iona.com>
uest@w3.org Subject: RE: WS-A Issue 28 - Multiple ports needed in an EPR
11/06/2004 04:54 PM
Hi Dave,
I understand the desire for simplicity. But if it's simplicity that you
want, why not forego the EPR entirely and use a URI? You stated your
opinion for why we need an EPR over just a URI in a separate thread. By
what criteria do you judge your need for an EPR rather than just a URI to
be acceptable, while judging our need for multi-address EPRs to be too
complicated?
Obviously you can raise all kinds of hypothetical complications regarding
multi-address or multi-mechanism services. In practice, it's really not
that complicated. Middleware has supported such constructs for well over a
decade now, the best example of which is probably the CORBA IOR. IORs may
consist of one or more profiles, where each profile may contain a separate
address, but all profiles in the same IOR "point" to the same target
object. In practice, most IORs consist of only a single IIOP profile, but
the flexibility for multiple profiles is there, and it's amazingly handy
when you need it.
If you want to keep the EPR simple, as you stated, are you instead
proposing that this WG also standardize some kind of composite EPR as well?
Because if this WG doesn't address the multi-address issue, then the
layering you're proposing will be strictly proprietary and
non-interoperable, and will proliferate the complication. I already pointed
out the problem with the layering approach in my reply to Gudge, and that
is that it just pushes the problem into the higher levels of software where
it has to be handled again and again and again, which makes it less likely
that it will be handled at all, which will result in rigid inflexible
systems that cannot deal with protocol, format, and service evolution.
Imagine, for example, if all IORs could contain only a single profile. That
would force all CORBA applications to be able to accept sequences of IORs
in all the places they would normally just accept a single
one-or-more-profile IOR. It forces all the complication up into the
applications. Do you really want to make your users' lives more
complicated?
--steve
-----Original Message-----
From: David Orchard [mailto:dorchard@bea.com]
Sent: Saturday, November 06, 2004 3:31 PM
To: Vinoski, Stephen; Martin Gudgin; Bergersen, Rebecca;
public-ws-addressing@w3.org
Cc: Newcomer, Eric
Subject: RE: WS-A Issue 28 - Multiple ports needed in an EPR
Steve,
I agree that in some indeed many cases there may be a need for
multiple "addresses" for a service. But don't we need an atomic
address at some point? I think we do have a pretty good handle on
what the minimum is to address a single "thing". I'd suggest that
any kind of multi-address construct can be layered on. And there
will be lots of complexity: What's the order of precedence? Are
there any commonalities, like policy across all the address? Are
there policies specific to an endpoint? Are there different
bindings/required properties per endpoint? I propose that
multi-address information should be layered on top and EPRs remain as
simple as we can keep them, rather than pushing the multi-stuff into
EPRs.
By analogy, I agree that molecules are great. And sometimes just
atoms are the thing we want, like gold or oxygen. The universe deals
well with both constructs, but they do have a layering/composition
model.
Another saying I like for standards is "you know your standard is
successful when people go great, but can you add foo, bar, baz..".
That means it hit the minimum necessary for success.
Cheers,
Dave
From: public-ws-addressing-request@w3.org
[mailto:public-ws-addressing-request@w3.org] On Behalf Of Vinoski,
Stephen
Sent: Friday, November 05, 2004 1:50 PM
To: Martin Gudgin; Bergersen, Rebecca; public-ws-addressing@w3.org
Cc: Newcomer, Eric
Subject: RE: WS-A Issue 28 - Multiple ports needed in an EPR
Gudge, take a look at your own business card. Does it have your
address, work phone number, fax number, mobile number, email address,
instant message ID, and your home page all listed on it, or do you
actually have multiple business cards, one listing your address, a
separate one listing your work phone, another listing your email
address, etc.?
You seem to imply that an endpoint is accessible via only a single
transport and protocol. Where I come from, endpoints can be accessed
over any number of transports and protocols. Why limit an EPR to
describing only a single path to an endpoint? There is much
middleware prior art in exsitence that proves that such a limit is
completely unnecessary.
--steve
-----Original Message-----
From: Martin Gudgin [mailto:mgudgin@microsoft.com]
Sent: Thursday, November 04, 2004 2:35 PM
To: Bergersen, Rebecca; public-ws-addressing@w3.org
Cc: Newcomer, Eric; Vinoski, Stephen
Subject: RE: WS-A Issue 28 - Multiple ports needed in an EPR
I take issue with the assertion "where there are different
protocols/transports/formats available for the same service,
the "access to a Web service endpoint" requires the client to
choose among alternatives".
If I, the service, give you, the client, a single EPR then as
far as you are concerned, there is only one mechansim with
which you can communicate with me. So you don't need to make
any choices ( except whether to communicate or not, I guess ).
If I am available on multiple EPRs, then I'll provide you with
multiple EPRs (perhaps in a WSDL document), *then* you have to
choose one from the set.
Gudge
From: public-ws-addressing-request@w3.org
[mailto:public-ws-addressing-request@w3.org] On Behalf Of
Bergersen, Rebecca
Sent: 04 November 2004 11:53
To: public-ws-addressing@w3.org
Cc: Newcomer, Eric; Vinoski, Stephen; Bergersen, Rebecca
Subject: WS-A Issue 28 - Multiple ports needed in an EPR
Issue 28 - Multiple ports needed in an EPR
According to the ws-addressing submission, "Endpoint
references convey the information needed to identify/reference
a Web service endpoint, and may be used in several different
ways: endpoint references are suitable for conveying the
information needed to access a Web service endpoint...."
However, in the situation where there are different
protocols/transports/formats available for the same service,
the "access to a Web service endpoint" requires the client to
choose among alternatives, each accessible in the standard
manner through a port - but there are different ports for each
protocol/transport/format alternative. When such alternatives
exist, the EPR must be able to identify those multiple ports.
Rebecca Bergersen
Principal Architect, Middleware Standards
rebecca.bergersen@iona.com
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Received on Sunday, 7 November 2004 04:28:46 UTC