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RE: On WSDL attributes

From: Martin Chapman <martin.chapman@oracle.com>
Date: Thu, 11 Sep 2003 09:08:07 -0700
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>
Message-ID: <000401c3787e$e39ff7f0$1faf2382@us.oracle.com>

What I find disturbing is that the group dismissed the rpc syntax (even
though it can be nicely layered on top of the basic message mechanism), and
at the same meeting seem to be more open to the more specialised attribute
syntax!

Martin.

> -----Original Message-----
> From: www-ws-desc-request@w3.org 
> [mailto:www-ws-desc-request@w3.org] On Behalf Of Sanjiva Weerawarana
> Sent: Wednesday, September 10, 2003 12:47 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 Thursday, 11 September 2003 12:08:11 GMT

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