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Subject: RE: [sca-bpel] Issue 3 - An amended proposal - Correlation Disagreement between SCA and BPEL proposal


 

My first inclination would be to have two different faults.  One fault that says we know, logically, that you have sent a faulty correlation set.  A different fault would be used to report that your seemingly valid correlation set hasn’t been matched by some designated timeout period (although I’m not sure which side should define that timeout).

 

If others feel strongly that these two error conditions should be combined into one fault, I would be OK with that, but my preference would be to keep them separate.  I’m also not sure that I would bother standardizing on the timeout fault, since it may be appropriate for it to be different for different bindings.  Essentially, this is an argument to keep it as “never”.

 

Michael

 


From: Alex Yiu [mailto:alex.yiu@oracle.com]
Sent: Wednesday, November 14, 2007 4:21 PM
To: Michael Rowley
Cc: Dieter Koenig1; Mike Edwards; Najeeb Andrabi; 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,

I understand your concern.

Wording versions:
Version 1: "will never be matched"
Version 2: "will not be matched"
Version 3: "can not be matched"

I think the current version 3 has the least interpretation space for the engine to queue up messages, because it loses the time dimension semantic.

Differences on whether to use the term "never":
Consider the case that: (one of the bullet in the proposed non-normative text)

·         matching IMAs blocked by other activities within a sequence

Say, a matching IMA is blocked by another preceding receive. Or, a matching IMA is blocked by an ill-defined preceding loop.

If we pick the term "never" in version 1, then using this standard fault to notify the message sender won't be covered by the if-condition. Because, the engine cannot logically conclude the external message for the blocking receive will never arrive or the engine cannot logically conclude the ill-defined loop will never finish.

My intention here is: the engine may notify the sender of this error condition, if a matching IMA cannot be found in a timely manner.

E.g. if a section of a process typically takes only few minutes or hours, after days or weeks of waiting for the blocking receive / loop, and, if the engine decides to notify the sender of this error condition by this new fault, it should be covered by the spec.

So, I prefer wordings of version 2 or a new version wording (modified based on version 3):
Version 4: "can not be matched ... in a timely manner"

Of course, the exact details of "timely manner" will depend on the underlying protocol (transport and coordination) and etc.

For example, if:

·         the operation is request-response

·         HTTP is the transport protocol (say the HTTP timeout is: 360 seconds)

·         an IMA cannot be matched within the transport timeout period

·         but a potential matching IMA is pending but not activated yet.

If we use the term "never", then this new standard fault does seem to be applied and the existing transport level time out fault will be applied instead. If we use wordings of version 2 or version 4, then this standard fault can be applied and covered by the spec.

Further thoughts and comments?

Thanks!


Regards,
Alex Yiu



Michael Rowley wrote:

The reason I had included the word "never" was precisely for this
reason.  I didn't want it to read that there is no IMA active right now.
I wanted to say that the system determined that there never would be
one.  There certainly are times when that can occur, such as when you
are using a combination of engine-managed correlation and explicit
correlation sets.
 
If we don't say "never", then I'm not sure how we would word this to
allow for queuing up messages until an IMA becomes active.
 
Michael
 
-----Original Message-----
From: Dieter Koenig1 [mailto:dieterkoenig@de.ibm.com] 
Sent: Tuesday, November 06, 2007 4:31 AM
To: Mike Edwards
Cc: alex.yiu@oracle.com; Najeeb Andrabi; sca-bpel@lists.oasis-open.org
Subject: Re: [sca-bpel] Issue 3 - An amended proposal - Correlation
Disagreement between SCA and BPEL proposal
 
Alex, Mike E, Mike R, Najeeb,
 
I assume we agree that we want to allow a BPEL implementation to store a
message if it can be consumed by a process instance at a later point in
time. Do we want to make this explicit in the normative language? (Of
course, it cannot be decided in many cases, and additional
considerations
apply - e.g., it makes a lot of sense for one-way messages and it makes
less sense for request-response operations called via synchronous
bindings
[<- btw, this is another scenario for issue BPEL-12]).
 
For those cases where we finally decide to return an
"sca:DeadLetterMessageError" fault to the sender, I have additional
questions:
 - in case of request-response operations, would this fault manifest
itself
as an SCA ServiceRuntimeException?
 - in case of one-way operations, will SCA (the assembly spec?) define
the
coordination protocol messages?
 
Kind Regards
DK
 
 
 
 
 
  From:       Mike Edwards <mike_edwards@uk.ibm.com>
 
 
 
  To:         sca-bpel@lists.oasis-open.org
 
 
 
  Cc:         Najeeb Andrabi <nandrabi@tibco.com>, alex.yiu@oracle.com
 
 
 
  Date:       06.11.2007 09:46
 
 
 
  Subject:    Re: [sca-bpel] Issue 3 - An amended proposal - Correlation
Disagreement between 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>
 
 
To 
                          Michael Rowley <mrowley@bea.com>
 
 05/11/2007 19:23
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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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
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