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   Re: [xml-dev] Categories of Web Service messages: data-oriented vs actio

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Roger proposes:

> I have convinced myself that there are two fundamentally different
> approaches to designing Web service XML messages.  They are:
> 1. The data-oriented approach
> 2. The action-oriented approach

It's not just Web Services that has this paradigm choice.  Client server has 
wrestled with Messaging vs RPC for a long time as well.  This seem to be just 
a continuation of the same debate.

Soap allows both paradigms, but it seems that RPC is the default modus 
operandi for many developers, probably since it looks like local method 
invocations and as such is easily understood.  The problem with RPC has 
always been that the developer loses sight of the fact that the calls are in fact 
network invocations and as such have massively larger latencies. This causes 
no end of problems when inexperienced developers use too fine a level of 

Messaging with it's Point to Point and Pub/Sub approaches tends not to suffer 
from this type of problem, since it is obvious to the developer when they are 
issuing network calls or not.  RPC also doesn't have the concept of Pub/Sub 
which is a very handy approach to many problems (you can do it with RPC, 
but have to roll your own).

Typically you also find that Action => RPC => Synchronous versus Data => 
Messaging => Asynchronous.  Many developers seem to want to avoid 
asynchronous processing, which is a shame since it tends to scale much more 
linearly than synchronous approaches (in general).

There is a good article on the evils of RPC that might be tangentially relevant 
to this whole topic:


Worth a read.  The author makes some interesting points about the evils of 
RPC, that apply to Web Services.

Andrzej Jan Taramina
Chaeron Corporation: Enterprise System Solutions


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