4 rule-based expert systems - school of computer science and 4基于规则的专家系统-计算机科学学院

《4 rule-based expert systems - school of computer science and 4基于规则的专家系统-计算机科学学院》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、4Rule-basedExpertSystemsArule-basedexpertsystemisanexpertsystem(seeintro)whichworksasaproductionsysteminwhichrulesencodeexpertknowledge.Mostexpertsystemsarerule-based.Alternativesareframe-based-knowledgeisassociatedwiththeobjectsofinterestandreasoningconsistsofconfirmingexpectations

2、forslotvalues.Suchsystemsoftenincluderulestoo.model-based,wheretheentiresystemmodelstherealworld,andthisdeepknowledgeisusedtoe.g.diagnoseequipmentmalfunctions,bycomparingmodelpredictedoutcomeswithactualobservedoutcomescase-based-previousexamples(cases)ofthetaskanditssolutionarestore

3、d.Tosolveanewproblemtheclosestmatchingcaseisretrieved,anditssolutionoranadaptationofitisproposedasthesolutiontothenewproblem.KBDSSIntro22LucyHedermanTypicalExpertSystemArchitecture(fromLugerandStubblefield)KBDSSIntro22LucyHedermanData-drivenRule-basedExpertSystemsUseForwardChaining:

4、GivenacertainsetoffactsinWM,usetherulestogeneratenewfactsuntilthedesiredgoalisreached.Toforwardchaintheinferenceenginemust:1.Matchtheconditionpatternsofrulesagainstfactsinworkingmemory.2.Ifthereismorethanonerulethatcouldbeused(thatcould"fire"),selectwhichonetoapply(thisiscalledconfl

5、ictresolution)3.Applytherule,maybecausingnewfactstobeaddedtoworkingmemory4.Haltwhensomeuseful(orgoal)conclusionisaddedtoWM(oruntilallpossibleconclusionshavebeendrawn.)KBDSSIntro22LucyHedermanGoal-drivenRule-basedExpertSystemsUseBackwardChaining:Workbackwardsfromahypothesisedgoal,att

6、emptingtoproveitbylinkingthegoaltotheinitialfacts.TobackwardchainfromagoalinWMtheinferenceenginemust:1.Selectruleswithconclusionsmatchingthegoal.2.Replacethegoalbytherule'spremises.Thesebecomesub-goals.3.Workbackwardstillallsub-goalsareknowntobetrue-eithertheyarefacts(inWM)ortheuser

7、providestheinformation.KBDSSIntro22LucyHedermanExampleAproductionsystemIDENTIFIER,whichidentifiesanimals.R1IFtheanimalhashairTHENitisamammalR2IFtheanimalgivesmilkTHENitisamammalR3IFtheanimalhasfeathersTHENitisabirdR4IFtheanimalfliestheanimallayseggsTHENitisabirdR5IFtheanimalisamamma

8、ltheanimaleatsmeatT