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   RE: [xml-dev] Categories of Web Service messages: data-oriented vs acti

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> From: Roger L. Costello [mailto:costello@mitre.org] 
> Questions:
> 1. I am having a really hard time understanding the later two 
> actions. 
> Of course I understand that a service would need to perform 
> these two actions, but I fail to understand why a "client" 
> would have to explicitly specify these actions in the XML 
> message.  Such "sub-actions" seem to be part of the semantics 
> of the umbrella "purchase-CD" action. 
> Can someone explain this to me?  Or, is it just a poor 
> example of a multi-action message?  If so, please give me a 
> better example.

These sub-actions within data; sound like you're trying to describe a
service 'process' or a sequence of 'events', over that data, and
doing/embedding that in a data 'instance' might be awkward. Here's
another perspective on process, from Drew McDermott:

Suppose I described buying a Coke as a DAML-S 
CompositeProcess, with two 'components',
PutInNickel and TakeOutCoke (if you find a 
machine that behaves like this, let me know).  
What I mean is that any instance of BuyACoke
consists of two parts, each of which is an 
intance of PutInNickel and TakeOutCoke.  But 
you won't see any actual instances until you get
down to particular stories, i.e., particular 
occasions when someone put in a nickel and got 
out a Coke.  It's a bit like programming-language 
semantics, where one might define ";" by saying 
"An event is of type "s1;s2" if and only if it 
consists of two consecutive events, the first of 
type s1 and the second of type s2."

The thread itself is an interesting one. 


Bill de hOra


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