Monotonic vs, non -monotonic Rules (2) Solution 2 R1: If birthday then special discount R2: If birthday is not known, then not special discount Solves the problem but The premise of rule R2 is not within the expressive power of predicate logic We need a new kind of rule system 10 Chapter 5 A Semantic Web primer10 Chapter 5 A Semantic Web Primer Monotonic vs. Non-monotonic Rules (2) Solution 2 R1: If birthday, then special discount R2’: If birthday is not known, then not special discount ⚫ Solves the problem but: – The premise of rule R2' is not within the expressive power of predicate logic – We need a new kind of rule system