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Re: DAML-S ProcessModel

From: Stanislaw Ambroszkiewicz <sambrosz@ipipan.waw.pl>
Date: Mon, 19 May 2003 20:46:36 +0200 (CEST)
Message-Id: <200305191846.h4JIkar27486@ns.ipipan.waw.pl>
To: sam@ksl.Stanford.EDU
Cc: www-ws@w3.org, agarwal@aifb.uni-karlsruhe.de

Dear Sheila,

You wrote: 
"The DAML-S process model is still a declarative description of a process.
Nevertheless the process is described in terms of procedural programming
language/workflow constructs such as "if-then-else", "while"  etc.. As
such, you can reason *about* the workflow/process using the DAML-S process
model description.  This description provides the requester with
the building blocks to have a conversation with the service -- an
exchange of messages.  A composite process can have many possible
execution trajectories, depending upon what messages are exchanged
(imagine all the different executions you could have with amazon.com,
depending upon what answers you gave to questions posed by the service).
By providing this composite process model, a requester can analyse what
answers it should give to questions to achieve a desired outcome.  This
is important for automated composition tasks, among other things. "

My reply:

There is another way to realize this using "pure" 
declarative approach like in Prolog. 
In this case "a composite process" has exactly one
"execution trajectory", however it has two phases: 
Query phase, and execution phase.
This may be sketched as follows. 

Query phase:
The requester specifies its "desired outcome", e.g., 
"I want to buy a book of J.R.R. Tolkien". 
In the cyberspace it means that "an invoice for a book 
of Tolkien is delivered to the requester". 
The "desired outcome" must be expressed in a common 
generic conversation language. 
(As far as I know there are no means to express 
explicitly the "desired outcome" in DAML-S)
The "desired outcome" is sent to bookstore.com. 
The bookstore.com has a look at its database and replies: 
"I will send you the invoice for a book of Tolkien, if
you send me an order where:
The title is 'The Lord of the Rings' and the price is 60 euro and ...
 or
the title is 'Hobbit' and the price is 30 euro  and ...
... 
This completes more or less the query phase. 

Execution phase: 
Once the requester receives the reply from the bookstore.com, 
it creates the order according to the options delivered by 
bookstore.com, fills some additional personal data to 
complete the order, and sends the order to the bookstore.com. 
(Of course, the choice made by the requester determines the 
execution path. However, it is done only by the requester 
who delivers the initial resources)
The bookstore.com creates appropriate invoice and sends it 
back to the requester. 
This completes more or less the execution phase. 
Note that transactions is missed, however it is no problem 
to extend this approach with a transaction phase. 

As to "the service type" I will explain my view in the next 
email if it is still of interest. 

Best regards,
Stanislaw,
 
 -- Stanislaw Ambroszkiewicz
 http://www.ipipan.waw.pl/mas/
Received on Monday, 19 May 2003 14:46:42 GMT

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