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

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

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

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

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.

Y can now be assumed to be true. 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.

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

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

Rule interpretation for forward reasoning Matching Conflict Execution

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.

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

Advantages Modularity Uniformity Naturalness