1. Copyright © 2002 Cycorp Errors with Constants, Variables, and Reliance on NL Errors with Specialization, Generalization, and Rules Other Errors Errors in Representing Knowledge

2. Copyright © 2002 Cycorp Over-generalization “Every organism has a head” Make more specific rules, e.g., for vertebrates, insects

3. Copyright © 2002 Cycorp Over-generalization “All people speak some language” State exceptions for infants, muteness

4. Copyright © 2002 Cycorp Over-generalization “Every person has some building or part of a building as their home” State in a Microtheory that assumes a modern culture.

5. Copyright © 2002 Cycorp Over-specialization Is this rule OK? “Every person is younger than his or her parents.”

6. Copyright © 2002 Cycorp Over-specialization Is this rule OK? “Every person is younger than his or her parents.” True, but what about dogs? Plants?

7. Copyright © 2002 Cycorp Over-specialization: Unnecessary Constraints Consider the following rule: (#$implies (#$and (#$isa ?MAST #$Mast) (#$physicalParts ?BOAT ?MAST) (#$isa ?BOAT #$Sailboat)) (#$rigidityOfObject ?MAST #$Rigid)) The second and third literals are unnecessary, and keep the rule from applying in all the cases that it should.

8. Copyright © 2002 Cycorp Non-modular Rules A fine rule: (#$implies (#$isa ?BOAT #$Sailboat) (#$thereExists ?MAST (#$and (#$isa ?MAST #$Mast) (#$physicalParts ?BOAT ?MAST))))

9. Copyright © 2002 Cycorp Non-modular Rules Bad: (#$implies (#$isa ?BOAT #$Sailboat) (#$thereExists ?MAST (#$thereExist ?HULL (#$and (#$isa ?MAST #$Mast) (#$isa ?HULL #$Hull-BoatPart) (#$physicalParts ?BOAT ?MAST) (#$physicalParts ?BOAT ?HULL))))) The existence of a sailboat’s hull is independent of the existence of its mast.

10. Copyright © 2002 Cycorp Non-modular Rules Better: Split into two (#$implies (#$isa ?BOAT #$Sailboat) (#$thereExists ?MAST (#$and (#$isa ?MAST #$Mast) (#$physicalParts ?BOAT ?MAST)))) (#$implies (#$isa ?BOAT #$Boat) (#$thereExists ?HULL (#$and (#$isa ?HULL #$Hull-BoatPart) (#$physicalParts ?BOAT ?HULL))))

11. Copyright © 2002 Cycorp Non-modular Rules What’s wrong here? (#$implies (#$isa ?BOAT #$Sailboat) (#$thereExists ?MAST (#$and (#$isa ?MAST #$Mast) (#$physicalParts ?BOAT ?MAST) (#$rigidityOfObject ?MAST #$Rigid)))) All masts are rigid, not just the mast which exists for each sailboat!

12. Copyright © 2002 Cycorp Non-modular Rules Better: (#$implies (#$isa ?BOAT #$Sailboat) (#$thereExists ?MAST (#$and (#$isa ?MAST #$Mast) (#$physicalParts ?BOAT ?MAST)))) (#$implies (#$isa ?MAST #$Mast) (#$rigidityOfObject ?MAST #$Rigid))

13. Copyright © 2002 Cycorp Avoid over-generalization –Choice of terms –Exceptions –Choice of microtheory Avoid over-specialization –Choice of terms –Unnecessary constraints Use Modular Rules Summary