RE: Composition as planning

At 0:51 +0100 2/2/04, Charlie Abela wrote:
>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

Charlie -
  easy example - suppose I call a service to see if Amazon has the 
book I want in stock.  I then complete the plan and move to execution 
- but while I was completing the plan someone else buys the last book 
in stock -- my plan now fails (esp. if this book was to be used as a 
precondition for something else) -- or when the credit check is done 
they say my number was wrong and the plan fails -- most AI planning 
assumes all execution is under the control of the planner -- also 
that operators execute instantly and without failure and lots of 
things like that --- there are some planners that can handle certain 
models of uncertainty and things like that, but none of thoe really 
work that well for Web Services...

p.s. If you're looking for a backgrounder on planning - Austin and I 
are two of the editors of the Readings in Planning book (James Allen 
is the third) which collects a lot of the seminal early papers on 
planning, and also has a couple of overview papers that will help you 
in learning the terminology of the AI literature.
-- 
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 23:04:28 UTC