B-Sure: A Believed Situation And Uncertain-Action Representation Environment

This paper l)reseltts a system that is c~q)abte of representing sit-us,loss, states, anci nondeterminlstic lIOIlinOllOtollic Oil'COllie actions ,lccmTillg ill multiple possible worlds. :['he systcnl sup ports explicit representations of actions and situations used in intentional action theory and situation theory. [lath types mid instances ere supported. Situations ¢md statc"a before a,d aftel-llOllll/OllOtOnic actions c~ul be repl'esellted shnultaneously. Agents have free will as to whether to choose to peiform an ac:-lion or not. Situations itud actions can have expected values, allowing the system to support decision making anti decision-based pleal isfferencing. The system cau perform global reasoning simultaneously across multiple possible worlds, without being forced to extend each world explicitly. The resulting system is useful for retch *tatural language t~-~ks a~ plan recognition , intentions modeling, attd parallel ta.~k scheduling. 1. Introduction The key to good reasoning is a powerful representation system that is able to accuratcly model details of a problem. Once a good represent.at,on has been established, problem computations often become straightforward. I¢~ecent advances in situation theory [BP83,Bax89] and the theory of intentions [Bra87] have offered ninny new insights on significant problems found in natural-language understanding. However, these the-aries offer philosophical approaches only, and do not give instructions for building concrete reprcsentation and reasoning engines. At the same time, the software systems that have been built for reasoning and representation fall short in any ruunber of areas. Production systems and semantic networks can follow chains of inferences, but can only represent one possible world at a time they cannot reason with states that are both possibly true and possibly not true, while keeping the chains of resulting inferences separatc. Most plasl-nets work with limited possible worlds, but callnot reason and perform inferences across multiple worlds at the salne time. The classical ATMS 1 call represent and reason with multiple timeless possible worlds, but calmot represent actions [dK86]-in particular, non-monotonic actions where a retracted state is both believed'to be truc in the world before ttte action