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RE: On WSDL attributes

From: VAMBENEPE,WILLIAM (HP-Cupertino,ex1) <vbp@hp.com>
Date: Wed, 10 Sep 2003 16:48:15 -0400
Message-ID: <68157FD469848D45B9CBC2833AD5528007348C9E@xsun02.ptp.hp.com>
To: 'Sanjiva Weerawarana' <sanjiva@watson.ibm.com>, Jeffrey Schlimmer <jeffsch@windows.microsoft.com>, Savas Parastatidis <Savas.Parastatidis@newcastle.ac.uk>, WS Description List <www-ws-desc@w3.org>


+1 to Sanjiva. In the proposal discussed at the F2F, the <attribute> element
under <interface> can be thought of as <operation variant="attribute"> or
something like that. This is another way to define messages exchanged.

William

> -----Original Message-----
> From: Sanjiva Weerawarana [mailto:sanjiva@watson.ibm.com] 
> Sent: Wednesday, September 10, 2003 12:48 PM
> To: Jeffrey Schlimmer; Savas Parastatidis; WS Description List
> Subject: Re: On WSDL attributes
> 
> 
> 
> 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:
> 
> http://lists.w3.org/Archives/Public/www-ws-desc/2003Jan/0005.html
> 
> 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).
> 
> Sanjiva.
> 
> ----- 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 16:48:51 GMT

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