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Re: On WSDL attributes

From: Sanjiva Weerawarana <sanjiva@watson.ibm.com>
Date: Thu, 11 Sep 2003 01:47:19 +0600
Message-ID: <035201c377d4$5a07ab50$72545ecb@lankabook2>
To: "Jeffrey Schlimmer" <jeffsch@windows.microsoft.com>, "Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>, "WS Description List" <www-ws-desc@w3.org>

If this was about state, I would be in 200% agreement. However,
I don't view attributes as a shortcut for exposing state.

As you noted, we must be careful about cross-platform
interoperability. The proposal we discussed briefly at the
last F2F was a way to view attributes as simply another
message exchange. There were NO new concepts added to the
underlying model of Web services: there are still only
messages going back and forth. The only difference was
that that WSDL would provide, in effect, a different
syntax for defining those messages.

I think the syntax we currently have for operations is a
bit lousy (and I think Savas or someone else suggested
changing it too). Back in January of this year I made a
proposal for a generalized syntax for message exchanges
as well as syntactic shortcuts for "standard" patterns:


If we do something like that then the simple input-output
and input-only patterns can be given simple syntax ala what
we have already (the proposal above suggests that too).
Furthermore, since attributes (at least the way I proposed
them at the F2F) are *not* new constructs but a different
way of specifying a set of messages, they too can have a
convenient syntax.

This does not amount to adding anything to the underlying
model of Web services being things that send and receive
messages nor does it bring up the dreaded question of
state(fullness or lessness).


----- Original Message -----
From: "Jeffrey Schlimmer" <jeffsch@windows.microsoft.com>
To: "Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>; "WS
Description List" <www-ws-desc@w3.org>
Sent: Thursday, September 11, 2003 1:19 AM
Subject: RE: On WSDL attributes

> Savas, we agree. General Web services do not need a first-class notion
> of persistent state associated with a service.
> Adding functionality to the Web service model necessarily implies
> additional constraints on underlying implementations. To facilitate
> cross-platform interoperability, we must be careful to minimize the
> architectural constraints on implementations. The current
> message-oriented definition of Web services appears to be an excellent
> tradeoff between function and minimal architectural commitment.
> There are communities who wish to associate state with service
> instances; our WG should ensure that they can do so through
> extensibility.
> --Jeff
> > -----Original Message-----
> > From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org]
> On
> > Behalf Of Savas Parastatidis
> > Sent: Tuesday, September 09, 2003 4:44 AM
> > To: WS Description List
> > Subject: On WSDL attributes
> >
> >
> > All,
> >
> > Here are some thoughts by Jim Webber and myself on the introduction of
> > attributes in WSDL...
> >
> >
> > The proposal on the introduction of attributes in the WSDL
> specification
> > has come a long way due to the work that the relevant Task Force has
> > produced. The most recent update to the proposal is, we believe,
> closer
> > to the WSDL way of describing message exchanges. However, it is so
> close
> > that we believe attributes are not necessary for WSDL.
> >
> > 1. Attributes represent a concept that it is not part of the Web
> > Services Architecture. Nowhere in the WSA document, to our knowledge,
> is
> > it suggested that a Web Service has attributes. Web Services send and
> > receive messages. They do not have operations, functions, methods, or
> > attributes as it is the case with object-based component models. WSDL
> is
> > used to describe messages that can be sent and received. The notion of
> > an "attribute" attempts to add a characteristic to Web Services that
> > simply does not exist.
> >
> > 2. The current version of the proposal defines particular message
> > exchange patterns. Since there is already work being carried out in
> this
> > area, we feel that there is no need for the introduction of attributes
> > in WSDL. For instance, the notion of a solicit-response MEP is
> somewhat
> > analogous to "getting" an attribute, while a request-only MEP is
> > analogous to "setting" an attribute. Given these abilities which are
> > already an accepted part of WSDL, this undermines the need for "read",
> > "read-write", and "write" qualifiers for attributes.
> >
> > To summarise: We believe that attributes are a fundamental property of
> > object-based systems, and do not have a corresponding use in SOA. We
> are
> > supported by WSA in this thinking. Furthermore, we believe that the
> > benefits of an attribute style interaction in terms of being able to
> > "set" or "get" structured XML data from a Web service is already
> > supported with WSDL operations.
> >
> > While we think that the work of the ATF is correct in itself, we would
> > oppose the inclusion of such work into WSDL, and would instead
> > anticipate that it would form part of some other specification which
> > leverages WSDL extensibility. Those communities which have a
> > demonstrated need to deploy Web services in a distributed object-like
> > scenario (e.g. Grid), can then utilise the separate attribute
> > specification to support their needs, without adding non-WSA features
> to
> > WSDL.
> >
> > Regards,
> > Jim Webber
> > Savas Parastatidis
> >
Received on Wednesday, 10 September 2003 15:47:56 UTC

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