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Subject: Issue 123 - Proposal for vote
The following contains some textual updates suggested in an email from Alex last week. No substantive changes were made.
Issue 123 - Proposed changes to current draft for scoped messageExchange:
In section 6.2 add to the informal syntax describing the XML grammar for both the process element and the scope element between partnerLinks and variables the following:
Change the following paragraphs from Section 11.4:
The optional messageExchange attribute is used to associate a <reply> activity with an inbound message activity, such as, <receive>, <onMessage> and <onEvent>, when there are multiple simultaneously incomplete inbound message activities which requires a reply message to complete.
A reply activity is associated with a inbound message activity based on the tuple - partnerLink, operation, and messageExchange. The value defined in messageExchange is scoped to the combination of partnerLink and operation. That is, it is legal to use the same messageExchange value in multiple simultaneously incomplete receive activities so long as the combination of partnerLink and operation on the receives are all different from each other. An incomplete inbound message activity describes the state of a BPEL process from the point that a request/response receive activity starts execution until its associated reply begins execution.
If there should ever be multiple simultaneous incomplete inbound message activities which have the same partnerLink, operation and messageExchange tuple then the bpws:conflictingRequest fault MUST be thrown within the BPEL process on the conflicting inbound message activities subsequent to the execution of the successful incomplete receive.
If a reply activity cannot be associated with an incomplete receive activity by matching the tuples and this error situation is not caught during static analysis, then bpws:missingRequest fault MUST be thrown within the BPEL process on the reply activity. Because conflicting requests should have been rejected at the time inbound message activity is executed, there cannot be more than one corresponding inbound message activity at the time <reply> is executed.
If the messageExchange attribute is not specified on a receive then its value is taken to be empty. For matching purposes two empty messageExchange values with the same partnerLink and operation values are said to match. Empty value does not match with other non-empty values.
To the following:
A reply activity is associated with an inbound message activity (IMA), such as, <receive>, <onMessage> and <onEvent> based on the tuple - partnerLink, operation, and messageExchange. The name used in the optional messageExchange attribute MUST resolve to a messageExchange declared in a scope (where the process is considered the root scope) which encloses the reply activity and its corresponding IMA. This resolution follows the same scoping rules as variable and correlationSet resolution.
An open IMA describes the state of a Web service operation from the point that a request/response IMA starts execution until an associated reply begins execution. It is illegal to have multiple simultaneous open IMAs, which have the same partnerLink, operation and messageExchange tuple. A BPEL process MUST throw a bpws:conflictingRequest fault when the conflicting IMA begins execution. Note that it is legal to use the same messageExchange in multiple simultaneously open IMAs so long as the combination of partnerLink and operation on the IMAs are all different from each other.
If a reply activity cannot be associated with an open IMA by matching the tuples (partnerLink, operation, and messageExchange) then a bpws:missingRequest fault MUST be thrown within the BPEL process on the reply activity. Because conflicting requests MUST be rejected at the time the IMA begins execution there cannot be more than one corresponding IMA at the time a reply activity is executed. Further if an open IMA goes out of scope prior to being closed by a reply activity then the scope MUST throw a bpws:missingReply fault. In other words a scope which declares a partnerLink or messageExchange used by an IMA will not complete normally if that IMA is open when the scope is to complete.
If the messageExchange attribute is not specified on an IMA or reply then the activity's messageExchange is automatically associated with a default message exchange with no name. Default message exchanges are implicitly declared by the process, onEvent scope and the immediate child scope of forEach activities marked as parallel. Default message exchange instances, just like non-default messages exchanges, are created each time the default message exchange provider is executed. For example each time an onEvent is executed (i.e. when a new message arrives for processing) it creates a new default message exchange instance associated with each onEvent instance. This prevents an onEvent handler, which doesn't specify a messageExchange, for request-reply operations from faulting when a message is received while there is already another instance of the onEvent handler processing a message that has not reached its reply point. Similarly it allows most parallel forEach receive(or pick)-reply pairs to be described without the need to introduce a messageExchange. The use of messageExchange for most applications is required only for cases where the execution of a flow can result in receives(or pick)-replies on the same partnerLink and operation executed simultaneously so the application must mark the relationship between the pairs.