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Modeling Belief Reasoning in Multi-Agent Systems*

Modeling Belief Reasoning in Multi-Agent Systems*. Thomas R. Ioerger Department of Computer Science Texas A&M University. *funding provided by a MURI grant through DoD/AFOSR. Many interactions in collaborative MAS require reasoning about beliefs of others

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Modeling Belief Reasoning in Multi-Agent Systems*

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  1. Modeling Belief Reasoning in Multi-Agent Systems* Thomas R. Ioerger Department of Computer Science Texas A&M University *funding provided by a MURI grant through DoD/AFOSR

  2. Many interactions in collaborative MAS require reasoning about beliefs of others There are no efficient, complete inference procedures for modal logics of belief Need a practical way of maintaining models of other agents beliefs Want it to work much like JARE Correct representation of unknown is a must New Issue: how do you know what others believe? various reasons of different strength Motivation

  3. Define hierarchy of justification types including: rules, defaults, persistence also incorporate observability a major source of info about others’ beliefs represent truth-values explicitly (T,F,?) update cycle (given current beliefs, senses...) BOA - Beliefs of Other Agents like JARE: syntax, binding envs, API, query, assert forward-chaining single-level of nesting: (bel joe (open door)) Approach

  4. Rule types (with strengths for resolving conflicts) 8 - assertions (e.g. from shell, perceptions, messages) 7 - facts (static, never change truth value) 6 - direct observation (self) 5 - effects of actions (for whoever is aware of it...) 4 - inferences (by any agent) 3 - observability (of others) 2 - persistence (“memory,” certain beliefs persist) 1 - default assumptions (given no other evidence) Justifications

  5. (infer (bel ?a (not (tank empty ?car)) (bel ?a (running ?car)) (persist (bel ?a (light-on ?room))) (obs ?a (light-on ?r) (in ?a ?r) (light-on ?r)) (effect (running ?c) (do ?a (start ?c)) (have ?a (keys ?c))) (default (unknown (wumpus alive))) (init (val (num-arrows) 3)) (infer (can-shoot)(val (num-arrows) ?x)(> ?x 0)) (obs (bel ?a (whether (light-on ?rm)) (in ?a ?rm)) (fact (bel archer (value-of (num-arrows)))) (fact (bel archer (whether (can-shoot)))) BOA Syntax consequent antecedent assume believer is ‘self’ context function procedural attachment

  6. What conclusions can be drawn from KB? Update cycle (hence forward chaining): KB’=update(KB,senses,action?,justification rules) If multiple rules relevant to a predicate can fire, want strongest to determine truth-value Must control order of firing, avoid premature... Semantics based on prioritized logic programs Brewka & Eiter, Sakama & Inoue, Delegrande & Schaub Sort predicates by antecedent dependencies fire all for rules for least-dependent predicate first Prioritized Inference no circularities allowed

  7. You get back a Vector of JareEnv’s with variable bindings for alternative solutions (as usual) (query (threat enemy-unit-17)) (query (val (target enemy-unit-17) ?target)) (query (bel sam (light-on room-1))) (query (bel joe (light-on ?r))) (query (bel joe (not (light-on room-1)))) (query (bel joe (whether (light-on room-1)))) Can’t use variable for agent name: (query (bel ?a (has-weapon ?a)))does not work! Queries in BOA

  8. Useful for writing plans that depend on what others believe Challenges: interaction with JARE and variable binding in conditions Preliminary experiments: method 1: separate JARE and BOA KB’s beliefs can’t be used as conds in IF, WHILE...; use bq-if method 2: replace JARE completely efficiency? - assert/retract used for many things in CAST Integration into CAST (?)

  9. (task inform-others-of-loc (?enemy) (seq (bupdate) (foreach ((agent ?ag)) (if (cond (gunner ?ag) (not (radio-silence))) (bq-if (bel ?ag (unknown (val (loc ?enemy))) (bq-if (val (loc ?enemy) ?loc) (seq (send ?ag (val (loc ?enemy) ?loc)) (bassert (bel ?ag (val (loc ?enemy) ?loc)) ))))))))

  10. Ryan’s experience useful for implementing Proactive Information Exchange in CAST-PM (Master’s thesis online) http://faculty.cs.tamu.edu/ioerger/thesi/rozich-thesis.pdf awkward to have to say that everything persists! Reflection on Belief Reasoning... not as expressive as Modal Logic, but efficient no nested beliefs the real issue is: managing the various reasons for beliefs about others’ beliefs (observability, actions, inference, defaults, persistence...) Concluding Remarks

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