- From: Charlie Abela <abcharl@keyworld.net>
- Date: Mon, 2 Feb 2004 00:51:01 +0100
- To: "Jim Hendler" <hendler@cs.umd.edu>, "Austin Tate" <a.tate@ed.ac.uk>
- Cc: <public-sws-ig@w3.org>
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