W3C home > Mailing lists > Public > public-sws-ig@w3.org > December 2004

Re: Planning under Description Logic ?--an obstacle towards WSAC

From: Drew McDermott <drew.mcdermott@yale.edu>
Date: Mon, 6 Dec 2004 13:16:00 -0500
Message-Id: <200412061816.iB6IG0hK017102@pantheon-po06.its.yale.edu>
To: public-sws-ig@w3.org


> [Manshan Lin]
> 1) SHOP2 approach seems to use a partially ordered set of tasks to
> describe the user's requirements. I don't think it's a feasible way
> comparing with goal formula.  Actually, the underlying intention of
> the abstract tasks are their outputs and effects, which are goal
> formulas. However, these goal formulas may be achieved by different
> abstract tasks.

I don't understand your point.

> 2) The HTN planning domain includes a set of operators (that is,
> atomic service) and a set of methods (that is, composite service). I
> don't know whether the process model of OWL-S intents to be shared
> among agents. But from the viewpoint of security, I thow doubt on
> the agents' willing to expose their process model, which may reflect
> their business logic.

The services don't expose their process models.  They expose a
client's _view_ of the process model.  That is, the steps of a
composite process are actions for the client to perform that will (in
the normal case) achieve the client's goals.

> 3) In [3], it extends HTN planning algorithm to handle
> incomplete-information planning problem. While some information can
> be provided by web services, some must be provided by the user
> himself since we can't require the user to provide all the needed
> information to accomplish the plan. The question is, how to
> distinguish what information should be provided by other web
> services and what should be provided by the user? As discussed in
> the mailing list before, since we can't control other services, the
> information gathered during planning may be different when
> executing. As mention at the end of the paper, I agree that
> inserting queries to the plan (leading conditional plans) is more
> proper.

I tend to agree that, in principle, information gathering should be a
planned activity, not an activity done before planning (and therefore
organized in a different way).  However, there is a caveat which
shrinks the difference between the two approaches.  It is in general
impractical, counterproductive, and (often) impossible to produce a
conditional plan that anticipates all the branches that might occur as
a result of gathering information.  Hence a planning algorithm must be
able to produce an incomplete plan, in which some --- maybe all ---
branches end with the note "If you reach this point, plan some more."
So planning, execution, and information gathering are inevitably
interleaved.

I should mention that no one, as far as I know, has a good theory of
when to stop elaborating conditional branches.

-- 

                                         -- Drew McDermott
                                            Yale University
                                            Computer Science Department

Some see the glass as half empty, some as half full.  Surely the
truth lies somewhere in between.
Received on Monday, 6 December 2004 18:16:01 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Sunday, 16 March 2008 00:10:59 GMT