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CS62S: Expert Systems

CS62S: Expert Systems. Based on: The Engineering of Knowledge-based Systems: Theory and Practice, A. J. Gonzalez and D. D. Dankel. Expert Systems Structure. Three perspectives: User Knowledge engineer Tool builder. User. Intelligent program User interface Problem specific database.

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CS62S: Expert Systems

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  1. CS62S: Expert Systems Based on: The Engineering of Knowledge-based Systems: Theory and Practice, A. J. Gonzalez and D. D. Dankel

  2. Expert Systems Structure • Three perspectives: • User • Knowledge engineer • Tool builder

  3. User • Intelligent program • User interface • Problem specific database

  4. Knowledge Engineer • Intelligent Program • Knowledge base • Inference engine • Development shell • Knowledge acquisition tool • Test case database • Developer’s interface

  5. Tool builder Concerned about providing appropriate Development Shell and Inference engine:

  6. Rule-based reasoning (part 1) IF-THEN • condition, premise, antecedent • action, conclusion, consequence

  7. Examples condition - action If you are approaching a traffic signal and it is red, then you should stop premise - conclusion If the sky is overcast, then it is going to rain antecedent - consequent If you leave your headlights on while the car engine is off, then your batteries will die.

  8. Inference Rule-based systems use modus ponens rule of inference to reason about facts and their relationship to the knowledge base. i.e. If X is known to be true and the relationship X->Y is true, then Y can now be assumed to be true.

  9. Rule-based vs Logic • Can be nonmonotonic (facts retraction) • Handle uncertainty

  10. Reasoning Process • Data driven • forward chaining • synthesis, design, configuration, planning, scheduling • Goal driven • backward chaining • diagnostic problems

  11. Rule interpretation for forward reasoning • Matching • Conflict • Execution

  12. Gonzalez and Dankel states the following steps for the interpreter: • Find all rules whose premises are true and mark them as being applicable. • If one or more rule applies, then deactivate any whose actions add a duplicate result to the database • Execute the action of the lowest numbered applicable rule. If none applies, then halt. • Reset the applicability of all rules and return to step 1.

  13. Disadvantages of rule-based systems: • Infinite chaining • Conflicting new rule • Modification • Inefficiency • Opacity • Coverage of domain

  14. Advantages • Modularity • Uniformity • Naturalness

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