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Enterprise Integration Patterns - issues

 
P Das
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1) Is it that "messaging" always subsumes a MOM? In such case, when we say, "Object X sends message to object Y" in the sense that X invokes a method of Y, the usage becomes confusing.

2) The above dilemma cause another conceptual issue: on page xxxiv and xxxv, the authors imply that messaging provides "reliable delivery that RPC cannot", which is further fortified with "store and forward" and "guaranteed delivery". Is it safe to say so in SCEA exam? I bring this on the table because, often there are questions on credit card authorization in the mock tests where the preferred answer is that messaging should not be used in such case.
 
Cameron Wallace McKenzie
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"Object X sends message to object Y"

Messaging is quite a bit different from invoking a method on another object. In fact, that doesn't really happen with messaging, certainly not directly, and it's actually debatable as to whether it happens indirectly.

I think each sequence in the process, 1) placing of the message and 2) reading of the message, must be treated as separate sequences.

Opinions?

-Cameron McKenzie
 
Ajay Singh Rathore
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I agree with Cameron, in case of messaging client interacts with the MOM and not with the consumers of the message, client has to make sure that it sends the message to the correct destination (queue or topic) and the delivery aspect is taken care by the MOM.

So this process of messaging takes place in two transaction and not one-from producer to MOM and from MOM to consumer, that's why if there is a requirement to have a sequence of operations to be executed in a single transaction then in that case messaging is not a desired solution.

Although if you want you can send the message, do some procesing and then wait for the reply from other end by listening to a destination all in a single transaction but that doesnt make much sense.

Thanks,
Ajay
SCJP, SCDJWS, SCEA 5 part 1
[ September 22, 2008: Message edited by: AJAY SINGH RATHORE ]
 
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