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LCW-Based Agent Planning for the Semantic Web

LCW-Based Agent Planning for the Semantic Web. Jeff Heflin, Hector Mu ñ oz-Avila presented by Axel Polleres cf. http://www.cse.lehigh.edu/~heflin/pubs/lcw-aaai02.pdf. Overview. Add LCW to DAML+OIL and SHOE Combine enriched ontologies with OTD.

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LCW-Based Agent Planning for the Semantic Web

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  1. LCW-Based Agent Planning for the Semantic Web Jeff Heflin, Hector Muñoz-Avila presented by Axel Polleres cf. http://www.cse.lehigh.edu/~heflin/pubs/lcw-aaai02.pdf

  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 r1, …, rn and nothing else! • i.e. DAML-LCW is not more expressive than DAML+OIL itself. • Problem: very naïve, since r1, …, rn 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.

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