Stateful message processing for async scenario

Question

Dear all,
my async scenarios:
1. RFC -> PI -> File
2. File  -> PI -> RFC
Following facts:
- The second message is a response to the first one. Both message are separted and async.
- Scenario 2 can be send some hours after Scenario1.
- A response should only be send if  a specified field in the message of first scenario is filled. 
  For example: Message in scenario has a field <ResponseNeeded>YES</ResponseNeeded>
  This field does only exist in message of scenario 1.
- Both message have an ID field (e.g. <ID>4711</ID>) which can be used to identified the
  corresponding message.
Questions:
- Is it possible to use stateful message processing for this scenario? Or do I need BMP + Correlation?
- A service interface with pattern "stateful" can only be used synchronously. So is it
  possible to use this stateful for async message processing at least?
I would assume that I will need a BPM that sends the messsage and keep alive until a
response will be sends with same ID. After this I would check message of scenario1 and
send (or even not) the message of scenario2 to receiver depending on <ResponseNeeded>.
Thanks in advanced.
Chris

Answer 1

Hi Chris,
Although BPM is possible here, I would not recommend you to use one here for the reason,
>>Scenario 2 can be send some hours after Scenario1.
This means you are keeping a process alive for so long which is not a good thing to do.
You could end up with a lot of open/live process instances.
Having said that, if you still wish to go ahead with BPM, the steps would be
1. Receive async (RFC req) - start process, correlation based on ID.
2. Switch step (Evaluate ResponseNeeded)
branch 1(True): a.  Send asynch step - File
                           b. Receive async - File correlation - ID.
                           c. Send async - RFC call.
branch 2(false) a. Send async -File
3. Stop process.
Regards
Jai