Knowledge-Representation-and-Reasoning---Villanova-University-维拉诺瓦大学知识表示与推理.pptVIP

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Knowledge-Representation-and-Reasoning---Villanova-University-维拉诺瓦大学知识表示与推理.ppt

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Knowledge Representation and ReasoningFocus on Sections 10.1-10.3, 10.6Guest Lecturer: Eric EatonUniversity of Maryland Baltimore CountyLockheed Martin Advanced Technology LaboratoriesAdapted from slides byTim Finin andMarie desJardins.Some material adopted from notes by Andreas Geyer-Schulz,and Chuck Dyer.1 OutlineApproaches to knowledge representationSituation calculusDeductive/logical methodsForward-chaining production rule systemsSemantic networksFrame-based systemsDescription logicsAbductive/uncertain methodsWhat’s abduction?Why do we need uncertainty?Bayesian reasoningOther methods: Default reasoning, rule-based methods, Dempster-Shafer theory, fuzzy reasoning2 IntroductionReal knowledge representation and reasoning systems come in several major varieties.These differ in their intended use, expressivity, features,…Some major families areLogic programming languagesTheorem proversRule-based or production systemsSemantic networksFrame-based representation languagesDatabases (deductive, relational, object-oriented, etc.)Constraint reasoning systemsDescription logicsBayesian networksEvidential reasoning3 Ontological EngineeringStructuring knowledge in a useful fashionAn ontology formally represents concepts in a domain and relationships between those conceptsUsing the proper representation is key!It can be the difference between success and failureOften costly to formally engineer domain knowledgeDomain experts (a.k.a. subject matter experts)Commercial ontology, e.g. Cyc (cyc/, opencyc.org/)4 Representing changeRepresenting change in the world in logic can be tricky.One way is just to change the KBAdd and delete sentences from the KB to reflect changesHow do we remember the past, or reason about changes?Situation calculus is another wayA situation is a snapshot of the world at some instant in timeWhen the agent performs an action A in situation S1, the result is a new situation S2.5 Situations6 Situation calculusA situation is a s