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Killing the Command message: should we use Events or Documents? (2007)

If we want to decouple a SOA system, we must get away from the notion of the remote procedure call. In other words, our services need to have as few "command" messages as we can get away with.

But if someone wants to add a new validation rule, that says we won't create invoices for customers in Germany because of a new import law that went into effect, where does that restriction go? It subscribed to the event, and therefore discovered it, but it needs to call back to the source system to get the actual data to act upon. I agree with you saying in the reply above: Basically, it is "big events" with "rule based filters" but that doesn't sound as catchy as "document messaging."

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