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Re: Fwd: Re: DAML-S ProcessModel

From: Bijan Parsia <bparsia@isr.umd.edu>
Date: Tue, 20 May 2003 04:22:58 -0400
To: www-ws@w3.org
Message-Id: <3b6aaffe.86dde2c8.81a3800@isrmail.isr.umd.edu>

Sorry if there's crap formatting. VPN not working for me so
I'm reduce to webmail :)

I'm going to hack out large bits.

Me == >>
Sudhir Agarwal <agarwal@aifb.uni-karlsruhe.de> == >

>> To support choreography, composition, simulation, verification
>> and similar activities.
>OK. And How? 

Well, the short answer is to direct you to the paper list on
the daml-s site.

> What is the difference between choreography and composition?

Gosh, yeah, that's rough. My best current take is that
choreography is a style of composition, thus choreogrpahy is a
subclass of composition. Choerography, on this model, would be
the composition of very loosely connected web services.

>> > Isn't it enough to have only AtomicProcess?
>> Nope.

Because, for one, AtomicProcess alone don't tell you how to
coordinate many of them. 

>> >Why should a web service
>> >provider show how his services works?
>> Because I, the client, might have need to coordinate with
>> different phases of some one of his services. For example, if
>> some step of the service requires feedback, authorization,
>> etc. from me, I might want to know when to look for such
>> requests. If it involves transfer of money, I may have fairly
>> complex arrangements to make for this.
>Requirements of a web service belong in the preconditions.

Maybe not all requirements. Maybe some things are modeled
better eleswhere. We are talking engineering tradeoffs, yes?
As far as I can tell, you didn't consider the needs I outlined

What if I *need*, or just *want*, to have fine grained
monitoring of the service your provide. I want *auditability*,
and *oversight*. I don't just want a progress bar.

Why do I want these things? Well, first, who cares as long as
I want them? But a rational reason is to coordinated with
other activities. If I'm supposed to pay *at a particular
point* I might want to delay the actual transfer of fund in my
*internal* accounts until the last second.

How do I get that in preconditions of an AtomicProcess?

> If a client only 
>what to know which services participate in a complex service,
it is enough to 
>specify a list of participating services.

Oh come on. Sure, *if* that's all they want to know. But I
explicitly pointed out that I may want to know *when*, or want
to know which one comes before the other. I may want to
simulate what the service does.

There are plenty of places where this Just Doesn't Make Sense,
but there seems to be places wehre it does.

> Why all these constructs like 
>if-then-else, while etc.?

See above.

There also definitely seems to be some sort of "customer"
demand. BPEL, WSCI, Web Services Choerography, even DAML-S. Do
you deny the demand?

[snip long stuff from me]

>how can a client run a web service, which is provided by
someone else?

If I supply a Process Model with a composite process, I could
be providing a *descriptiong* of MY workflow, or I might
provide a detailed enough workflow/program that *you* could
run it (i.e., calling out to the atomic process but executing
hte conditionals, etc. in your own interpreter; that's how
most DAML-S CompositeProcesses are workign now)

>what do u mean by distributedly?

I mean that the CompositeProcess might describe complex MEPs
(see the DOPE semantics in terms of petri nets in Sheila's
papers for some ideas).

>  DAML-S uses WSDL for grounding. WSDL is 
>mostly used to specify SOAP, Java RMI, EJB web services. None
of them allows 
>to distribute a complex plan.

Er..Doens't that exactly point to a need supplied by
CompositeProcesses? It's exactly that *they* don't that we
have a need.


Bijan Parsia.
Received on Tuesday, 20 May 2003 04:23:08 UTC

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