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Subject: Re: [sca-bpel] Issue 3 - An amended proposal - Correlation Disagreementbetween SCA and BPEL proposal



Alex,

I agree with your point about "never", but I don't like your additional words in parentheses at all.  The extra qualifiication just complicates things needlessly
- let us leave it to the SCA & BPEL infrastructure to work out whether matching can be done.  I changed "will" to "can" as well, to get rid of this flavour of
"future-ness" in the wording which is not appropriate, since this statement is about a state and what to do when this state is detected.

How about:

“If the SCA or BPEL infrastructure is able to determine that a message, that has been sent to an endpoint address of a business process, can not be matched with a corresponding inbound message activity (i.e. receive, onMessage or onEvent), then:"

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



Alex Yiu <alex.yiu@oracle.com>

05/11/2007 19:23

To
Michael Rowley <mrowley@bea.com>
cc
Najeeb Andrabi <nandrabi@tibco.com>, sca-bpel@lists.oasis-open.org, ALEX.YIU@oracle.com
Subject
Re: [sca-bpel] Issue 3 - An amended proposal - Correlation Disagreement between SCA and BPEL proposal






Hi, Michael,

Thanks for the quick feedback.
I agree with you that the "if" condition in the normative text can be tightened up. I like your changes in general.

I am wondering whether the word "never" may be a bit too strong. I am thinking to use the word with a weaker tone with extra qualification description.

How about:
“If the SCA or BPEL infrastructure is able to determine that a message
, that has been sent to an endpoint address of a business process, will not be matched with a corresponding inbound message activity (i.e. receive, onMessage or onEvent) (possibly based on a message protocol or some infrastructure heuristic), then:"


If the extra qualification description "(possibly based on a message protocol or some infrastructure heuristic)" opens new cans of worms, I am comfortable to drop it.


Thanks!


Regards,
Alex Yiu


Michael Rowley wrote:

Alex,
 
Thanks for the background material.  I also the proposed normative text, except for the reference to “a dead letter message”, without having a definition for that in our spec.  I also thought that “message receiver” might be too vague.  Perhaps the first sentence, which you had as:
 
“If the SCA and BPEL infrastructure of the message receiver is able to detect a dead letter message:”
 
could instead read:
 
“If the SCA or BPEL infrastructure is able to determine that a message that has been sent to an endpoint address of a business process will never match a corresponding inbound message activity (i.e. receive, onMessage or onEvent), then:
 
Michael
 
 



From: Alex Yiu [mailto:alex.yiu@oracle.com]
Sent:
Thursday, November 01, 2007 12:34 PM
To:
Najeeb Andrabi
Cc:
sca-bpel@lists.oasis-open.org; ALEX.YIU@oracle.com
Subject:
Re: [sca-bpel] Issue 3 - An amended proposal - Correlation Disagreement between SCA and BPEL proposal

 

Hi all,

Here is an amended proposal for this Issue 3.

I believe the spirit of the proposal is the same. But, wordings and details are different. This amended proposal avoids/addresses a few issues that the original proposal has:

        "bpel:correlationViolation" is for BPEL's CorrelationSet lifecycle violation - not CS mismatch. I am not sure we want to overload it. All existing "bpel:*" fault thrown are for internally consumption only. Not directly visible through BPEL partnerLink.
        There is no formal notion of "wrapping" in WS fault.
        We need to address the difference in one-way or request-response MEP.
        The flow chart has "wait until all the IMA in all existing processes have been activated". That seems to be not so feasible / well-fit.
The proposal has two parts: background (non-normative) text and normative text.

If the background text is too long for some audience, I am happy to trim and para-phrase it. I send this longer version for the benefit for the TC discussion.

About the normative text, I hope it is short yet concise.
One thing to highlight is: it may be infeasible to specify a universal dead letter detection algorithm, which has real values to users. Hence, I am using SHOULD and MAY here, instead of MUST.

------------------------------------
[background text begins here ...]

When an inbound message comes into the SCA and BPEL infrastructure, such a message is normally consumed by a matching inbound message activity (IMA)(e.g. a <receive> activity). However, due to process model error or runtime message data error, there is no matching IMA at all or a matching IMA is not enabled within the expected time limit of the (system/business level) protocol between the message sender and receiver. This kind of messages, which do not have a matching IMA, are termed as "dead message messages"

Examples of process model error are:

        matching IMAs are skipped by faults
        matching IMAs blocked by other activities within a sequence or an impossible-to-fulfill control link transition condition.
        IMAs cannot receive message due to incorrect usage of message correlation mechanism, including BPEL correlation set and SCA conversational interface
Examples of runtime message data error are similar to above, as the above error are not inside the process definition itself but caused by incorrect data values.

There might not be a universal way to determine a message is truly a "dead letter message" without any additional protocol between message senders and receivers. Consider the following example, an message is dispatched to a BPEL process instance by SCA conversational mechanism. At the moment when the message is matched with the BPEL process instance, there might be no <receive> activity enabled for the matching partnerLink and operation at all, or there is a <receive> activity enabled for the matching partnerLink and operation but with a mismatched correlation set. Some users might think this is certainly a dead letter message situation. However, a matching IMA may be enabled minutes, hours, or days later, as the matching IMA might be blocked in the process model.

On the other hand, there might be some cases that the BPEL infrastructure can determine there will never be a matching IMA enable in future. And, some advanced features in BPEL infrastructure (e.g. process instance repair or process definition repair) might make the detection of "dead letter message" cases more difficult. However, with some additional system-level protocol coordination between the message sender and receiver, it might make detection easier.
------------------------------------

------------------------------------
[normative text begins here ...]

If the SCA and BPEL infrastructure of the message receiver is able to detect a dead letter message:

        If the message is sent through a request-response operation, "sca:DeadLetterMessageError" fault SHOULD be thrown to the message sender
        If the message is sent through a one-way operation and additional system-level protocol is  used between the message sender and receiver, the dead letter message error situation MAY be notified to the message sender, according to the protocol used.
------------------------------------


Looking forward to further comments and fine-tuning.

Thanks!



Regards,
Alex Yiu









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