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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 Jeff Heflin, Hector Muñoz-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. • Semantic Description of the involved Sources/Services is not an issue.
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 .
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.
DAML-LCW: State that a resource has complete information on a particular class.
DAML-LCW • Limited suitability for properties: Can express LCW(prop(X,c)), but not LCW(prop(c,X)), nor LCW(prop(x,y))
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.
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)
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)
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.
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)
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).
Querying the SWeb Mediator: Bound by resource-constraints such as time limits or max number of sources to be queried.
LCW yielding operators: After execution with f 355 and date 1/2/2002, we can add LCW(SeatFree(355, 1/2/2002, s))
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.