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Article: Building Asynchronous Services With SCA

by Mark Little on Jan 24, 2008 |
The Service Component Architecture has generated a lot of debate since its initial release in 2005. Although there has been a lot written about the actual specifications, there has been little on what a developer would be presented with. In this exclusive InfoQ article, Mike Edwards from IBM and one of the co-authors of the specifications, writes about how to develop asynchronous services using SCA.

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Confused. by An Phu

>For the OrderClient, there is a reference with the name "OrderService". On the OrderService there is a service with the name "OrderService".



This naming convention made it a little difficult to follow sometimes. I had to re-read the subsequent sentences to figure out whether you were referring to the client or service.



>The reference is connected to the service by a wire...



Connected by a wire?



>The fact that the connection involves a callback is defined by the interface used to describe the service...



So, a dual interface is an interface with both the service and callback interfaces?



>The presence of a element on both the OrderClient reference and on the OrderService service indicates that Web services are the method used to communicate between them.



What element? Are you referring to the <binding.ws/>?



It seems the scenarios for SCA can also be handled by asynchronous client processing with a message queue binding. Although there is more infrastructure involved with asynchronous client process, you get durability and robustness. The client does not need to be online all the time. With SCA, the client has to be available in order for the service to send back the response. what happens to the response message if the client callback is unavailable?

Re: Confused. by mike prendergast

"It seems the scenarios for SCA can also be handled by asynchronous client processing with a message queue binding. Although there is more infrastructure involved with asynchronous client process, you get durability and robustness. The client does not need to be online all the time. With SCA, the client has to be available in order for the service to send back the response. what happens to the response message if the client callback is unavailable?"

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The key point here is that you could do this with an async messaging implemenation where you manage the infrastructure. By using sca you let sca manage that for you and in fact in the IBM products it will generate MDBs etc later on during deployment.
However this is an async call as well asa response so in fact the client doesn't have to be present at the same time. For more detail on error handling see
www.ibm.com/developerworks/websphere/library/te...
You may want to print it out

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