OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.

 


Help: OASIS Mailing Lists Help | MarkMail Help

sca-j message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]


Subject: RE: [sca-j] ISSUE 25 - Callback Simplification


Simon,

 

I am certainly willing to give up any automatic correlation when there may be multiple simultaneous outstanding callbacks.  In that case, use business data.

 

However, for the common case where there is only one outstanding callback for a specific client, then your approach already allows the client to know what the callback is talking about without passing any correlation information in the business data.  This is because your approach routes the callback to the right client instance.

 

I think this is good.  We should encourage it.  However, in the unfortunate event that someone can’t use a conversational-scoped client, they should still be able to use the bi-directional service without having to ask the service provider to change its interface.  Admittedly, the stateless client will have to implement many of the steps that you list below, but that is the price for being non-conversational.

 

I also believe that if we followed your suggestion, then no matter what we say, people just won’t send unneeded correlation information as business data when they know that the callback is going to be sent to the right place.  They won’t think: “Oh, just in case I ever have a stateless client, I better put this extra data into the business data.”  Instead, they will just leave out the data, with the unintended consequence being that they’ve limited their clients to being only those that use a conversational scope.  That would be bad.

 

Michael

 

 


From: Simon Nash [mailto:NASH@uk.ibm.com]
Sent: Thursday, April 03, 2008 12:13 PM
To: Michael Rowley
Cc: sca-j@lists.oasis-open.org
Subject: RE: [sca-j] ISSUE 25 - Callback Simplification

 


There's a basic problem with this approach.  Whether or not B has conversational scope depends on its interactions with A.  In a single A to B conversation, the same conversational instance of B might place 5 orders with C.  Using the A to B conversation ID to identify the order that was placed is therefore never safe, even if B is conversational.

The only way this approach could work is if B were to generate a new "callback conversation ID" for every request that it sends to C.  This would be different from any regular conversation ID that B may be sending to C as part of a B to C conversation.  Here are the steps that would need to be followed.

1. B generates a new "callback conversation ID" and associates it with its reference for C.  This needs to happen before any calls to C are made.
2. An API needs to be defined to allow B to get this "callback conversation ID" before it makes the placeOrder() call to C.  B stores the "callback conversation ID" and associates it with the order it is placing.
3. B makes a placeOrder() call to C.
4. The SCA infrastructure transmits the "callback conversation ID" from B to C with the placeOrder() call.
5. C stores the "callback conversation ID" in the callback reference so that it can be returned to B in any callbacks.
6. C makes a callback to B.
7. The SCA infrastructure transmits the "callback conversation ID" from C to B with the callback.
8. An API needs to be defined to allow B to get this "callback conversation ID" when the callback is executing.  This ID is different from the conversation ID that's active for the A to B conversation.

All of the above are not needed if the correlation information is passed as business data, which is a much simpler approach.

I considered this approach when I was trying to come up with a good definition of conversational callback interfaces between the 3/20 and 3/27 calls, but I rejected it because I did not believe that the value justified the complexity.

    Simon

Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156  Fax +44-1962-818999


"Michael Rowley" <mnrowley@gmail.com>

03/04/2008 15:40

Please respond to
mrowley@bea.com

To

Simon Nash/UK/IBM@IBMGB, sca-j@lists.oasis-open.org

cc

 

Subject

RE: [sca-j] ISSUE 25 - Callback Simplification

 

 

 



I like the fact that, in Simon's model, callbacks always go back to the instance that made the outbound call.  However, it looks like he does not take advantage of that fact in the interfaces of the examples that he created.  For example, he has the following:

 

@Callback(OrderCallback.class)

public interface Order {

            void placeOrder(String orderID, String orderData);

}

public interface OrderCallback {

            void confirm(String orderID);

            void update(String orderID, String status);

}

 

However, since you know that the order callback goes back to the right instance, you should be able to define the callback interface as follows:

 

public interface OrderCallback {

            void confirm();

            void update(String status);

}

 

In Simon's model this should be possible, but there is a catch.  If the callback interface is defined this way, the client has to use a conversational scope.  If the client is stateless or composite scoped, then the routing of the callback to the right instance doesn't say anything useful about what is being confirmed.

I would like to enable this style of callback interface irrespective of the scope of the client.  As with Simon's approach, if the client is conversational scoped, then the client is especially simple and does not have to do any correlation at all.  However, if the client needs to use some other scope, for whatever reason, then the service with the callback can still be used.  However, it just needs to get the callback ID (or conversation ID) that is associated with the callback in order to determine what the callback is talking about.

 

Michael

 


From: Simon Nash [mailto:NASH@uk.ibm.com]
Sent:
Thursday, March 27, 2008 11:47 AM
To:
sca-j@lists.oasis-open.org
Subject:
Re: [sca-j] ISSUE 25 - Callback Simplification

 

There's an update to this proposal at


http://www.oasis-open.org/apps/org/workgroup/sca-j/download.php/27733/JAVA-25-Proposal-2.doc

This version removes conversational callbacks as all my attempts to define these involve more complexity than is justified by the functional value of this capability.


   Simon


Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156  Fax +44-1962-818999

Simon Nash/UK/IBM@IBMGB

20/03/2008 11:01

 

To

sca-j@lists.oasis-open.org

cc

 

Subject

[sca-j] ISSUE 25 - Callback Simplification

 

 

 

 






Last week I took an action to produce a written up proposal for callback simplification by today.  I have uploaded this to the document repository as

http://www.oasis-open.org/apps/org/workgroup/sca-j/download.php/27649/JAVA-25-Proposal.doc.

The content of this proposal corresponds to the "Callback Simplification" section of the proposal sent out by Michael R, and does not address the changes proposed in the "API Simplification" section.  I think it is best to have these discussions separately.


This proposal corresponds to what I was describing at the sca-j F2F with two changes / additions:


1. Outstanding callbacks don't pin conversational objects after the conversation's creator has ended the conversation.


2. In all cases, the caller of a bidirectional interface creates the callback EPR that will be used (including any reference parameters needed).    


I believe the issues that still need to be discussed and resolved are as follows:


a) Should all 4 combinations of conversational and non-conversational forward and callback interfaces be allowed, or only 2 of these?


b) Should the callback interface used to make callbacks to a conversation-scoped component be marked as conversational?


c) Should each forward request within a conversation generate a unique ID that is not part of business data and is returned with the callback?


  Simon


Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156  Fax +44-1962-818999


 

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU








 

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU








 

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU







[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]