Knowledge Representationand Inference

CS 480/580Fall 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