1 LCW-Based Agent Planning for the Semantic Web Jeff Heflin, Hector Muñoz-Avila presented by Axel Polleres cf.

2 Overview Add LCW to DAML+OIL and SHOE Combine enriched ontologies with OTD. Semantic Description of the involved Sources/Services is not an issue.

3 Local Closed World Assumption An expression of the form LCW(  ) means stating that any substitution of  which is true in the real world is also represented in the agents knowledge, i.e. stating "local complete knowledge" on .

4 Semantic Web and LCW Why is this interesting here? The open world causes often unbounded search (therefore, e.g. classical planning is not directly applicable). Suggestion: Extend fixed KB by a “Semantic Web Mediator” to gather more information.

5 DAML-LCW: State that a resource has complete information on a particular class.

6 DAML-LCW Limited suitability for properties: Can express LCW(prop(X,c)), but not LCW(prop(c,X)), nor LCW(prop(x,y))

7 LCW within DAML+OIL States that C is the class of r 1, …, r n and nothing else! i.e. DAML-LCW is not more expressive than DAML+OIL itself. Problem: very naïve, since r 1, …, r n have to be enumerated explicitely.

8 SHOE-LCW states LCW(flight(X)  destination(X,Y)  USCity(Y)) LCW restricted to pos. conjunctions. more flexible than DAML-LCW (variables), but LCW not expressible within the language itself (complement/disjointness not expressible)

9 SHOE-LCW LCW adds implicit negation to SHOE. How to handle this? Non- monotonic reasoning? Unsolved. In the paper they assume “well-formed LCW information”, but can this be achieved in the Web? further remark: LCW cannot be defined on sets of resources (neither in DAML-LCW, nor in SHOE-LCW)

10 Rest of the paper OTD enhanced by Semantic Web mediator: What is OTD? method M(h,P,ST)... compound task definition with head h, preconditions P and a set of subtasks ST. matches(h,t,S)... a task matches a method with head h if hΘ=t and S satisfies PΘ where Θ is a substitution. operator O(h,P,aL,dL)... primitive action, with preconditions add-list and delete-list (like in STRIPS) OTD: match tasks to subtasks recursively to an ordered list of operators p, binding all parameters.

11 Architecture: Fixed KB contains information gathered so far (including LCW information) and domain theory. Other information sources queried via Semantic Web mediator. (Problem: offline, actions are not “executed” on the source before planning is completed)

12 LCW in planning: LCW information can arise in two forms in Planning: – LCW provided by information sources – LCW inferred as result of an action (example: UNIX command " ls " whereafter we know all files in a directory and we know that these are all files there).

13 Use LCW for precondition evaluation:

14 Querying the SWeb Mediator: Bound by resource-constraints such as time limits or max number of sources to be queried.

15 LCW yielding operators: After execution with f  355 and date  1/2/2002, we can add LCW(SeatFree(355, 1/2/2002, s))

16 Conclusions LCW can be udes to reduce/cut-off search space in search/planning. LCW info stored explicitly or yielded by action execution Unclear how to deal with inconsistent LCW information.