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Subject: Re: [sca-bindings] ISSUE-22: Callbacks for binding.ws

There is a profound and simple difference, in my understanding, between 
a callback operation invocation message
and a response message.

The callback operation is defined on a different interface from the 
original operation it is associated with, while
a response is defined in the same interface.

In my opinion, ws addressing replyTo could be used in an operation 
invocation message either to indicate
to where a callback (not defined as part of the operation signature) 
should be sent, or to indicate where a response
(defined as part of the operation signature) should be sent. The 
difference is in the way the interfaces are defined.

If a callback originator has enough knowledge to know the difference 
between a callback invocation and sending a
"normal" response to an operation, so could the callback receiver. Thus 
it does not seem necessary to differentiate
the two using different relatesTo values, since both parties would know, 
by the definition of the interfaces being used,
whether it is a callback message of a replyTo.

Tom Rutt

Michael Rowley wrote:
> I’d like to get this topic started. I’ve narrowed the subject line 
> from the original Issue 22 title, since I’d like this particular 
> thread to be on how callbacks could be handled in the WS-* world. We 
> can handle conversations and other bindings on other threads.
> First, I’ll assume that we will try to use WS-Addressing 
> <http://www.w3.org/TR/2006/REC-ws-addr-core-20060509/>, if possible.
> My first thought is that it would be preferable to be able to leverage 
> the ws-ReplyTo field, since I believe that it should be possible to 
> distinguish replies from callbacks, and I also believe that callbacks 
> should go to the same place that replies would go to. I have a vague 
> recollection that Anish preferred the use of <wsa:from> rather than 
> <wsa:replyTo> for passing callback ID information. Unfortunately, I 
> can’t find an email to that effect, so I’ll ask that he confirm or 
> deny that.
> I've been thinking that the client that is going to receive callbacks 
> might want the reference parameters that would be available if the 
> service provider follows the rules from the "Formulating a Reply 
> Message" section of the WS-addressing spec.
> One way that a callback could be distinguished from a reply is that 
> the callback could have a <relatesTo> header that uses a relationship 
> type of "oasis.org/isCallbackFor" and a reference to the messageID 
> that the callback is in response to. I haven’t seen other uses of the 
> <relatesTo> header, but it seems like this is exactly the sort of 
> thing it is meant for.
> Michael
> ------------------------------------------------------------------------
> *From:* Eric Johnson [mailto:eric@tibco.com]
> *Sent:* Monday, February 04, 2008 2:45 PM
> *To:* Mike Edwards
> *Cc:* OASIS Bindings
> *Subject:* Re: [sca-bindings] ISSUE-22: The Bindings specifications 
> should provide exemplary Implementations for a) Callbacks and b) 
> Conversations
> Logged as http://www.osoa.org/jira/browse/BINDINGS-22
> -Eric.
> Mike Edwards wrote:
> Raiser: Mike Edwards
> Target: Web Services Binding specification, JMS Binding Specification, 
> JCA Binding Specification
> Description:
> At present, it is not clear which, if any, of the Bindings 
> specifications enable the implementation of two important
> features of SCA described in the Assembly specification - namely 
> Callback interfaces and Conversational
> interfaces.
> Each of the Bindings specifications should explicitly declare if it is 
> possible to support each of these features.
> For each of the Bindings specifications that claim to support either 
> or both of these features, the specification
> should provide a full description of at least one exemplary 
> implementation of the feature using the Binding
> technology described in the specification. Multiple alternative 
> implementations are permitted and may be
> added to the specification.
> For example, it may be possible to implement Callbacks using 
> WS-Addressing capabilities with Web services.
> If so, and example, showing the use of appropriate features of 
> WS-Addressing and other relevant WS-*
> capabilities should be added to the specification. If an alternative 
> exists using (say) WS-Context, then an
> example based on that technology can also be provided.
> Proposal:
> None at present.
> Yours, Mike.
> Strategist - Emerging Technologies, SCA & SDO.
> Co Chair OASIS SCA Assembly TC.
> IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
> Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
> Email: mike_edwards@uk.ibm.com <mailto:mike_edwards@uk.ibm.com>
> ------------------------------------------------------------------------
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Tom Rutt	email: tom@coastin.com; trutt@us.fujitsu.com
Tel: +1 732 801 5744          Fax: +1 732 774 5133

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