Knowledge Representation and Inference CS 480/580 Fall 2009
Requirements for Knowledge Representation Languages Well-defined syntax and semantics General requirements: Representational adequacy Inferential adequacy Inferential efficiency Clear syntax and semantics Naturalness
Semantic Networks Originally developed in 1960s to represent the meaning of English words
Frames Frames are a variant of semantic networks Widely used in expert systems Semantic networks and frames are interchangeable Defaults and multiple inheritance Slots and procedures
Predicate Logic This is the most important knowledge representation Syntax: P V Q P ^ Q ¬Q P → Q P ↔ Q P ^ (Q → R); (Q V ¬R) → P
Predicate Logic (cont.) Notation: Begin with lower case letters for constants; Begin with a capital letter for variables; fatherof(allison, richard) Prolog uses , : and ;: OR More on Prolog …
Rule-based Systems If – then rules and facts Forward chaining system Conflict resolution Backward chaining system