CS62S: Expert Systems

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CS62S Expert Systems

• Based on
• The Engineering of Knowledge-based Systems
  Theory and Practice,
• A. J. Gonzalez and D. D. Dankel

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Expert Systems Structure

• Three perspectives
• User
• Knowledge engineer
• Tool builder

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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
• Developers interface

5
Tool builder

• Concerned about providing appropriate Development
  Shell and Inference engine

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Rule-based reasoning (part 1)

• IF-THEN
• condition, premise, antecedent
• action, conclusion, consequence

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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.

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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-gtY is true, then
• Y can now be assumed to be true.

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Rule-based vs Logic

• Can be nonmonotonic (facts retraction)
• Handle uncertainty

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Reasoning Process

• Data driven
• forward chaining
• synthesis, design, configuration, planning,
  scheduling
• Goal driven
• backward chaining
• diagnostic problems

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Rule interpretation for forward reasoning

• Matching
• Conflict
• Execution

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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.

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Disadvantages of rule-based systems

• Infinite chaining
• Conflicting new rule
• Modification
• Inefficiency
• Opacity
• Coverage of domain

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Advantages

• Modularity
• Uniformity
• Naturalness