General question about messaging and lost updates

I’m new to BizTalk and messaging systems, so sorry in advance for his newbie post.

I’d like to build an integration environment on BTS where systems that hold the master record, say for an employee, can publish adds, updates and deletes to various consumer/subscriber systems that care about records of that sort.

Now, part of the problem I’m having is that I’m not sure how to deal with cases where the record contains information whose constituent elements come from different systems. For example, our SAP system has an HR master record with say, first name, last name etc. It \”owns\” that information. However, Active Directory/Exchange owns the employee’s email address. Both of these information elements are part of the employee record, they just originate from different systems.

So, what happens when an AD/Exchange account is created [u:2ffe1899cf]before[/u:2ffe1899cf] the SAP HR master record even exists? A message flows from AD to BTS, and since SAP is subscribing to that message it gets a copy; but when it goes to update, there is no corresponding master record (based on some foreign key, like employee number.) How would I handle this? I don’t want to just ignore the message, because eventually, when the SAP record [url]is[/url] created, I want it to be updated with the email address from AD. But where do I put it and how would I resend it? From AD’s perspective the update occurred and it sent its message. To be loosely coupled, it should only care about sending out the changes: fire and forget. So I can’t have AD deal with the problem. And I really don’t want to create a separate holding area for these kinds of messages: it seems to me that this is a common enough problem that BTS must offer some kind of solution.

Thanks for the help.