RE: Composition as planning

Thanks for the information Jim. Even though it will take some time for me to digest all you said,
since I am just beginning to experiment with the planning research area. Nonetheless I find it's an
extremely interesting area and its close coupling with web services makes it even more a real issue
to tackle.

I can understand the issue of scalability, which the presented solutions that aim at providing
composition as planning, have to some extent bypassed by having a sort of closed world where all the
services are available or at least their location the world is already known, thus avoiding the
planner the burden of choosing from among a list of contenders.

Also the services, possibly returned by some service registry, would not all be ideal for being
composed. Maybe matching services would in future return a list of services whose ranking is based
on some composability measure together with input/output, precondition/effect matching (or subsumed
concepts of these).

I could not fully understand your point: (the assumption that change occurs only through the
operators under the control of this planner is clearly wrong)
OK STRIP's operators planning can just approximate some of the planning required in web services
compositions but imho, isn't the planning problem here related to:
a. Some service whose action (given some pre-condition and effect) fits into a sequence of other
services. It will just have to fill in a hole in the process. What's important is that it satisfies
some defined constraints such as QoS issues and that its effects, though suitable, do not interfere
with the process being executed.
b. Some possible means of the planner to replan in case some service, which should be executing,
fails for some reason.

I hope I am not being too shallow in my reply, but again I am just trying to understand basic
concepts here.

-------------------------------------------------
Charlie Abela


-----Original Message-----
From: Jim Hendler [mailto:hendler@cs.umd.edu]
Sent: Sunday, February 01, 2004 10:15 PM
To: Austin Tate; Charlie Abela
Cc: public-sws-ig@w3.org
Subject: RE: Composition as planning

I would point out that the mapping of web services to compositions
has largely been done in the past, even in the best work in this
area, with some simplifications that generally "twist" web services
into a planning framework -- there's huge parts of the web service
world that need to be explored before we can really say AI planning
has shown a success in web services other than as an evocative idea
--  the reason is that a real web services engine will need to deal
with (at least):
   - scaling issues way beyond anything we've seen in planning to date
(there may be thousands of services each with multiple ports,
optional arguments, etc.)
   - the issues Dana mentioned (side effects, change in the world,
etc.) that make Strips-operators planning an approximation at best
(the assumption that change occurs only through the operators under
the control of this planner is clearly wrong)
   - issues of interaction with users - web service planning better be
mre mixed-initiative
   - issues of preferences v. constraints
   - issues of interaction between planning agents out there (you buy
the book I'm in the process of planning to buy)
    - knowledge engineering issues (when planners take ebXML and WSDL
as inputs, instead of requiring specialized planning-like langauges
like Owl-S, then we'll see a lot more excitement on the outside -
OWL-S is an interesting starting place,  but we fool ourselves if we
think it really is going to be widely used for process specification
in its current form)
   In fact, I'll wager that it will be absolutely trivial to prove
that web services planning, even w/simplifications, is inherently
undecidable, so we'll need to explore a lot of the issues from the
old "dynamic planning" world as well
   All this, by the way,  I see as good news - it means this is a
fertile and exciting research area for those of us in planning, with
good heuristic solutions being transitionable.

That said, in the past I have tried to get AI planning people to
think outside the box and failed miserably, and I'll be surprised if
the web services planning stuff doesn't become an "applied" area
being ignored by the bulk of the research community (who, if you'll
apologize my saying so, still have their heads up their
you-know-whats worrying about scaling simple problems in all the
wrong ways)
   Forgive my pessimism, but the planning community has spent many
years resisting change - I don't see why just because we have a new
and potentially revolutionary problem that could expand the field
greatly, the leopards will change their spots...
  -Jim Hendler
p.s. Of course, I also think the Sem Web will be largely ignored by
traditional AI types until it kicks them in the head, so maybe this
is just more of the same :->
--
Professor James Hendler                   http://www.cs.umd.edu/users/hendler
Director, Semantic Web and Agent Technologies     301-405-2696
Maryland Information and Network Dynamics Lab.    301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742          240-277-3388 (Cell)

Received on Sunday, 1 February 2004 18:49:09 UTC