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 Development shell
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. 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.

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

10. Reasoning Process Data driven Goal 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