- To implement a synchronous web service operation. The process begins with an input message, runs through a quick burst of logic to process it, sends back the output message, and completes. The client application blocks for the duration, as diagram (a) in the next figure shows. If the process moves too slowly, the client will complain about the response time.
- To perform complex routing for the ESB. As David Chapelle discusses in his book Enterprise Service Bus (O’Reilly, 2004), a good ESB can natively perform basic content-based- and itinerary-based-routing, but it needs orchestration processes to handle more complex routing patterns. In diagram (b) in the figure, when the ESB receives a message, it passes it to an orchestration process that proceeds to perform in eight steps a series of transformation and invocation maneuvers that could never be achieved with the basic branching capabilities of the ESB. Again, speed is critical. The ESB prefers to get rid of messages as soon as it gets them. When it delegates work to an orchestration process, it expects that process to move quickly and lightly.
Having developed an approach to keep SOA processes running for an arbitrarily long time, we now turn our attention to short-running processes and ask: howcan we make them run as fast as possible? The two most common uses of a short-running process are:
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