Re: Composition as planning

At 09:08 PM 31/01/2004 +0800, you wrote:
>Does anyone know of work that compares the composition of web services 
>with the
>classical planning problem and which describes which concepts in planning are
>valid and which others need to be modified or added (if any)?

We are working on that area Charlie. See also work on SHOP2 at Maryland, 
and the work of Blythe/Gil and others at USC/ISI.

If you take recent practical planners as a basis, they already allow for:

a) specification of an outline process or requirements in the form of an 
initial plan including some aspects of state requirements and some aspects 
of activity performance in any combination desired.

b) they can take a library of process descriptions in the form of other 
partial plans, standard operating procedures, or descriptions of activities 
that are considered executable (no further refinement is known from the 
library anyway).

c) they can then automatically, or with user guidance or control refine the 
initial outline plan using the library of components to get a more detailed 
plan... going as far as you wish at plan time.

d) they can then support execution and execution monitoring of the partial 
plans, making selections of undecided parts at run time.

e) they can spot variance to the expected and required outcomes of 
activities and start plan repair processes to recover dynamically.

O-Plan is an instance of such a 
planner...  http://www.aiai.ed.ac.uk/project/oplan/
Its actually been running over the web in demo mode since 1995 using an 
HTTP style service interface from other applications and a web style user 
interface using CGI scripts (it predates work on more recent standards for 
such things).
    * Tate, A. and Dalton, J. (2003) O-Plan: a Common Lisp Planning Web 
Service, invited paper, in Proceedings of the International Lisp Conference 
2003, October 12-25, 2003, New York, NY, USA, October 12-15, 2003.
http://www.aiai.ed.ac.uk/project/ix/documents/2003/2003-luc-tate-oplan-web.pdf


We are now, within the DAML program, working on its successor I-Plan that 
sits within the I-X Process Panel framework and will assist with the 
general support to multi-agent planning and replanning.  But its also being 
created to act as a web services composition 
tool.  http://www.aiai.ed.ac.uk/project/ix/

The principal differences that I see in what we need to do to make this 
kind of AI planning useful in a web services context is to have some idea 
of how to decide what service descriptions to use at plan time and which to 
use (or discover) at execute time.  There is little point planning in fine 
detail a long time before you understand something of the execution 
context.  This is not a simple problem!  You need to have some model of the 
likely execution context at plan time.  This could be quite different if 
the composition is done ahead of time for verification and checking... to 
the case where its composed dynamically immediately ahead of execution and 
you can assume pretty much the same environment for both planning and 
execution (except for recover issues if the situation changes).

Our target for the I-Plan work in the DAML program is described in a AAAI 
Spring 2004 Symposium Web Services workshop paper. That's our only paper 
referring to this current research at the moment.  This describes how we 
will use I-Plan to compose semantic and grid services workflows that can be 
checked by IHMC's KAoS system for likely run time policy violations (and 
other analyses) ahead of actual execution in which these policies will be 
enforced by policy management services.
    * Uszok, A., Bradshaw, J.M., Jeffers, R., Johnson, M., Tate, A., 
Dalton, J. and Aitken, S. (2004) Policy and Contract Management for 
Semantic Web Services, AAAI Spring Symposium, Stanford University, 
California, USA, March 2004
http://www.aiai.ed.ac.uk/project/ix/documents/2004/2004-aaai-spring-uszok-sws.pdf

The richness of process/services description that can be used by such AI 
planners will only come into their own if the OWL-S/SWSL/SWS languages of 
the future support a moderately rich process model. NIST PSL is a possible 
base for this process model in SWSL and would give an extendible framework 
that would fit very well with the approach of using AI planning and 
execution recovery methods in web services composition and enactment. We 
are inputting to that effort by promoting our simple abstract and very 
extensible framework for process models called <I-N-C-A> (Issues, Nodes, 
Constraints and Annotations).

Best wishes, Austin










--
Prof. Austin Tate, Artificial Intelligence Applications Institute, Informatics,
University of Edinburgh, Appleton Tower, Crichton Street, Edinburgh EH8 9LE, UK
Tel: +44 131 650 2732 Fax: +44 131 650 6513 E-mail: a.tate@ed.ac.uk

Received on Saturday, 31 January 2004 09:08:54 UTC