Re: Idempotency attribute (Section 7.6.4.2, line 1569)

[christopher ferris <chris.ferris@east.sun.com>]

Arvola,

As Marty has already responded, the document exchange is an abstract
notion of the CPP/A that relates to information that is useful to the MSH.
It doesn't define the MSH, nor is it intended to do so.

As to idempotency, even in the absence of reliable messaging, providing
for some manner of idempotency check is useful. As to whether it is sensible
for one to define:

> What is the meaning of  deliverySemantics=OnceAndOnlyOnce and
> idempotency=false?
> 

it would be meaningless as you cannot achieve onceAndOnlyOnce without
idempotency. In the CPP/A spec, the example at line 1538 uses this
combination, and IMHO that should be fixed in the errata to be:

<ReliableMessaging deliverySemantics="OnceAndOnlyOnce"
	idempotency="true"
	messageOrderSemantics="Guaranteed">
...
</ReliableMessaging>

Also, a constraint should be added to the CPP/A spec in section 7.6.4.2
that precludes the combination you cited. However, this constraint cannot be
modelled in the XML Schema definition itself and would need to be externally 
enforced through some mechanism other than schema validation. It is likely that
RELAX-NG or possibly schematron could be used to express this manner of constraint.

 Martin W Sachs wrote:
> 
> Arvola,
> 
> To answer the simple question first:  The document exchange layer of the
> CPP-CPA contains the variables related to the Message Service.
> 
> As to idempotency, I hope that Chris Ferris will reply.  I believe that you
> have turned up another loose end from the TP-TRP interlocks during the
> first life of ebXML.  It certainly seems that idempotency checking cannot
> be optional with onceAndOnlyOnce semantics.
> 
> Regards,
> Marty
> 
> *************************************************************************************
> 
> Martin W. Sachs
> IBM T. J. Watson Research Center
> P. O. B. 704
> Yorktown Hts, NY 10598
> 914-784-7287;  IBM tie line 863-7287
> Notes address:  Martin W Sachs/Watson/IBM
> Internet address:  mwsachs @ us.ibm.com
> *************************************************************************************
> 
> Arvola Chan <arvola@tibco.com> on 07/26/2001 05:27:49 PM
> 
> To:   ebxml-cppa@lists.oasis-open.org
> cc:
> Subject:  Idempotency attribute (Section 7.6.4.2, line 1569)
> 
> This concept is not mentioned any where in the  Messaging Service spec. In
> order to implement the OnceAndOnlyOnce delivery  semantics, the MSH already
> performs duplicate detection and filtering. It is not  clear how the
> idempotency test applied at the document exchange layer (described  on line
> 1575) differs from the duplicate detection and handling described in
> Section 10.3 in the Messaging Service spec.
> 
> Is the document exchange layer part of the  MSH?
> 
> What is the meaning of  deliverySemantics=OnceAndOnlyOnce and
> idempotency=false?
> 
> -Arvola
> 
> Arvola Chan (arvola@tibco.com)
> TIBCO Software  (on loan to RosettaNet)
> +1-650-846-5046 (US-Pacific)
> 
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