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Subject: RE: [ebxml-msg] Sequences and sequence sharing


-----Original Message-----
From: Pim van der Eijk [mailto:pvde@sonnenglanz.net] 
Sent: Tuesday, September 02, 2008 1:08 PM
To: ebxml-msg@lists.oasis-open.org
Subject: [ebxml-msg] Sequences and sequence sharing


To follow up on the discussion on (re-)using sequences from two weeks
which ebMS messages are sent on the same WSRM sequence? This is more
about ebMS 3.0 in general than about multihop.

Jacques mentioned a default assumption that each Pmode is associated
with a distinct sequence.

<JD> I should have been more nuanced:
Core V3 says (B.2.1): "It is RECOMMENDED that all messages transmitted
over a same sequence use the same MPC. This becomes a requirement for
the In-Order reliability contract."
So messages from an RM sequence should not go over several MPCs, but the
reverse is not a problem: several RM sequences can use the same MPC.
The constraint is more about RM sequence vs. MPC, rather than Pmode.
Now, each leg of an MEP in a Pmode is assigned to only one MPC so far (I
ignore here the case of "sub-channels" of an MPC). But an MPC can easily
be shared by several Pmodes.
The key point about RM sequences, is that (B.2.1) we require that the
same Delivery Assurance(Ordering, At-Least-Once....) be used for all
messages of the same sequence. Given this, a Pmode could share a
sequence (and an MPC) with other Pmodes, and also a Pmode (which is
usually associated with a single Deliv Assurance, at least for each one
of its "legs") can still make use of several RM sequences for a single
"leg" - e.g. a pool of sequences - provided they are associated with
same delivery assurance.</JD>

1) In the document on routing examples
t_id=28981) I discuss a number of routing scenarios. The simplest case
assumes routing is based on To:PartyId only.  It basically asserts for
an I-Cloud that any ebMS message, including messages to be sent
reliably, is
handled by the same final MSH.   This means that an ebMS MSH can
its sequence creation, as some Pmodes can use the same sequence. It was
suggested to leave this out of the multihop specification and leave this
to implementers as it is an optimization rather than a potential
conformance or
interoperability issue.   

2) Section 2.5 mentions a situation where a message is routed
differently based on a message property value. This means that there
have to be different sequences based only on property values.  Can there
be two Pmodes that are the same except for a particular message property

<JD> I think so.

If not, the routing document should not refer to routing based on

3) The ebMS 2.0 message ordering module associates ordering with
ConversationId. Do we want to support a similar model with ebMS 3.0?  If
we have a business process where "conversations" consist of a
action, followed by one or more "ChangeOrder" actions followed by an
option "CancelOrder" action and they are to be processed in order, then
the MSH must use the same sequence to send them.  How and where is this

<JD> I think we have in the Pmode some way to associate a conversation
with a delivery assurance.
See Pmode.Reliability.Correlation and the like.


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